Re: Make the git codebase thread-safe
On Mon, Apr 1, 2019 at 10:07 PM Duy Nguyen wrote: > > On Tue, Apr 2, 2019 at 7:52 AM Matheus Tavares > wrote: > > I downloaded chromium to give it a try and got (on a machine with i7 and > > SSD, running Manjaro Linux): > > > > - 17s on blame for a file with long history[2] > > - 2m on blame for a huge file[3] > > - 15s on log for both [2] and [3] > > - 1s for git status > > > > It seems quite a lot, especially with SSD, IMO. > > There have been a couple of optimizations that are probably still not > enabled by default because they only benefit large repos. So you may > want to check and turn them on before measuring anything: > commit-graph, pack bitmap, untracked cache or fsmonitor. All these > should be mentioned in 'git help config' (as starting point). Also > search "threads" in that man page because some commands may have multi > threads support but disabled by default for the same reason. Nice, thanks for the suggestions! > From your command list though, I think you might get the same results > (maybe with a bit faster 'git status') even with all optimizations on. Yes, you were right. With the optimizations on, I got the following times on those same files: - 17~18s on blame for about_flags.cc - 1m50s~2m on blame for sqlite3.c - 15s on log for both - 0.3~0.5s on git status > -- > Duy
Re: Make the git codebase thread-safe
Duy Nguyen writes: > On Tue, Apr 2, 2019 at 5:30 PM David Kastrup wrote: >> >> Duy Nguyen writes: >> >> > On Tue, Apr 2, 2019 at 7:52 AM Matheus Tavares >> > wrote: >> >> I downloaded chromium to give it a try and got (on a machine with i7 and >> >> SSD, running Manjaro Linux): >> >> >> >> - 17s on blame for a file with long history[2] >> >> - 2m on blame for a huge file[3] >> >> - 15s on log for both [2] and [3] >> >> - 1s for git status >> >> >> >> It seems quite a lot, especially with SSD, IMO. >> > >> > There have been a couple of optimizations that are probably still not >> > enabled by default because they only benefit large repos. >> >> I've proposed a trivial change in 2014 that could have cut down typical >> blame times significantly but nobody was interested in testing and >> committing it, and it is conceivable that in limited-memory situations >> it might warrant some accounting/mitigation for weird histories (not >> that there isn't other code like that). > > I didn't really read the patch (I don't know much about blame.c to > really contribute anything there). But a quick "git blame --show-stats > unpack-trees.c" shows this > > Without the patch: > > num read blob: 767 > num get patch: 425 > num commits: 343 > > With the patch: > > num read blob: 419 > num get patch: 425 > num commits: 343 > > That's a nice reduction of blob reading. On a typical small file, the > actual time saving might be not much. But it could really help when > you blame a large file. > > Perhaps you could resubmit it again for inclusion? (at least a > sign-off-by is missing then) I don't expect it to go anywhere but will do. Feel free to herd it. -- David Kastrup
Re: Make the git codebase thread-safe
On Tue, Apr 2, 2019 at 5:30 PM David Kastrup wrote: > > Duy Nguyen writes: > > > On Tue, Apr 2, 2019 at 7:52 AM Matheus Tavares > > wrote: > >> I downloaded chromium to give it a try and got (on a machine with i7 and > >> SSD, running Manjaro Linux): > >> > >> - 17s on blame for a file with long history[2] > >> - 2m on blame for a huge file[3] > >> - 15s on log for both [2] and [3] > >> - 1s for git status > >> > >> It seems quite a lot, especially with SSD, IMO. > > > > There have been a couple of optimizations that are probably still not > > enabled by default because they only benefit large repos. > > I've proposed a trivial change in 2014 that could have cut down typical > blame times significantly but nobody was interested in testing and > committing it, and it is conceivable that in limited-memory situations > it might warrant some accounting/mitigation for weird histories (not > that there isn't other code like that). I didn't really read the patch (I don't know much about blame.c to really contribute anything there). But a quick "git blame --show-stats unpack-trees.c" shows this Without the patch: num read blob: 767 num get patch: 425 num commits: 343 With the patch: num read blob: 419 num get patch: 425 num commits: 343 That's a nice reduction of blob reading. On a typical small file, the actual time saving might be not much. But it could really help when you blame a large file. Perhaps you could resubmit it again for inclusion? (at least a sign-off-by is missing then) > Rebased/appended. > > -- > David Kastrup -- Duy
Re: Make the git codebase thread-safe
Duy Nguyen writes:
> On Tue, Apr 2, 2019 at 7:52 AM Matheus Tavares
> wrote:
>> I downloaded chromium to give it a try and got (on a machine with i7 and
>> SSD, running Manjaro Linux):
>>
>> - 17s on blame for a file with long history[2]
>> - 2m on blame for a huge file[3]
>> - 15s on log for both [2] and [3]
>> - 1s for git status
>>
>> It seems quite a lot, especially with SSD, IMO.
>
> There have been a couple of optimizations that are probably still not
> enabled by default because they only benefit large repos.
I've proposed a trivial change in 2014 that could have cut down typical
blame times significantly but nobody was interested in testing and
committing it, and it is conceivable that in limited-memory situations
it might warrant some accounting/mitigation for weird histories (not
that there isn't other code like that).
Rebased/appended.
--
David Kastrup
>From a076daf13d144cb74ae5fd7250445bbfb4669a05 Mon Sep 17 00:00:00 2001
From: David Kastrup
Date: Sun, 2 Feb 2014 18:33:35 +0100
Subject: [PATCH] blame.c: don't drop origin blobs as eagerly
When a parent blob already has chunks queued up for blaming, dropping
the blob at the end of one blame step will cause it to get reloaded
right away, doubling the amount of I/O and unpacking when processing a
linear history.
Keeping such parent blobs in memory seems like a reasonable optimization
that should incur additional memory pressure mostly when processing the
merges from old branches.
---
blame.c | 3 ++-
1 file changed, 2 insertions(+), 1 deletion(-)
diff --git a/blame.c b/blame.c
index 5c07dec190..c11c516921 100644
--- a/blame.c
+++ b/blame.c
@@ -1562,7 +1562,8 @@ static void pass_blame(struct blame_scoreboard *sb, struct blame_origin *origin,
}
for (i = 0; i < num_sg; i++) {
if (sg_origin[i]) {
- drop_origin_blob(sg_origin[i]);
+ if (!sg_origin[i]->suspects)
+drop_origin_blob(sg_origin[i]);
blame_origin_decref(sg_origin[i]);
}
}
--
2.20.1
Re: Make the git codebase thread-safe
On Tue, Apr 2, 2019 at 7:52 AM Matheus Tavares wrote: > I downloaded chromium to give it a try and got (on a machine with i7 and > SSD, running Manjaro Linux): > > - 17s on blame for a file with long history[2] > - 2m on blame for a huge file[3] > - 15s on log for both [2] and [3] > - 1s for git status > > It seems quite a lot, especially with SSD, IMO. There have been a couple of optimizations that are probably still not enabled by default because they only benefit large repos. So you may want to check and turn them on before measuring anything: commit-graph, pack bitmap, untracked cache or fsmonitor. All these should be mentioned in 'git help config' (as starting point). Also search "threads" in that man page because some commands may have multi threads support but disabled by default for the same reason. >From your command list though, I think you might get the same results (maybe with a bit faster 'git status') even with all optimizations on. -- Duy
Re: Make the git codebase thread-safe
Hi, I am planning to work on making pack access thread-safe as my GSoC project, and after that, parallelize git blame or checkout. Or even use the thread-safe pack access to improve the already parallel grep or pack-objects. With this in mind, I would like to know if the problem discussed in this thread[1] is still an issue on the repos you folks work with (gentoo, chromium, etc.). And also, could you please let me know which git commands did you find to me more problematic in them, nowadays? I downloaded chromium to give it a try and got (on a machine with i7 and SSD, running Manjaro Linux): - 17s on blame for a file with long history[2] - 2m on blame for a huge file[3] - 15s on log for both [2] and [3] - 1s for git status It seems quite a lot, especially with SSD, IMO. [1] https://public-inbox.org/git/CA+TurHgyUK5sfCKrK+3xY8AeOg0t66vEvFxX=jia9wxww7e...@mail.gmail.com/ [2] ./chrome/browser/about_flags.cc (same with ./DEPS) [3] third_party/sqlite/amalgamation/sqlite3.c (7.5M) Best, Matheus Tavares
Re: Make the git codebase thread-safe
It shouldn't be hard for us to run some tests with this patch applied. Will report back in a day or two. On Tue, Feb 18, 2014 at 9:55 AM, Junio C Hamano wrote: > Duy Nguyen writes: > >> On Sat, Feb 15, 2014 at 8:15 AM, Zachary Turner wrote: >> ... >>> 2) Use TLS as you suggest and have one fd per pack thread. Probably >>> the most complicated code change (at least for me, being a first-time >>> contributor) >> >> It's not so complicated. I suggested a patch [1] before (surprise!). >> ... >> [1] http://article.gmane.org/gmane.comp.version-control.git/196042 > > That message is at the tail end of the discussion. I wonder why > nothing came out of it back then. > > While I do not see anything glaringly wrong with the change from a > quick glance over it, it would be nice to hear how well it performs > on their platform from Windows folks. > > Thanks. -- To unsubscribe from this list: send the line "unsubscribe git" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
Re: Make the git codebase thread-safe
Duy Nguyen writes: > On Sat, Feb 15, 2014 at 8:15 AM, Zachary Turner wrote: > ... >> 2) Use TLS as you suggest and have one fd per pack thread. Probably >> the most complicated code change (at least for me, being a first-time >> contributor) > > It's not so complicated. I suggested a patch [1] before (surprise!). > ... > [1] http://article.gmane.org/gmane.comp.version-control.git/196042 That message is at the tail end of the discussion. I wonder why nothing came out of it back then. While I do not see anything glaringly wrong with the change from a quick glance over it, it would be nice to hear how well it performs on their platform from Windows folks. Thanks. -- To unsubscribe from this list: send the line "unsubscribe git" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
Re: Make the git codebase thread-safe
On Sat, Feb 15, 2014 at 8:15 AM, Zachary Turner wrote: > Even if we make that change to use TLS for this case, the > implementation of pread() will still change in such a way that the > semantics of pread() are different on Windows. Is that ok? > > Just to summarize, here's the viable approaches I've seen discussed so far: > > 1) Use _WINVER at compile time to select either a thread-safe or > non-thread-safe implementation of pread. This is the easiest possible > code change, but would necessitate 2 binary distributions of git for > windows. > 2) Use TLS as you suggest and have one fd per pack thread. Probably > the most complicated code change (at least for me, being a first-time > contributor) It's not so complicated. I suggested a patch [1] before (surprise!). > 3) Use Karsten's suggested implementation from earlier in the thread. > Seems to work, but it's a little confusing from a readability > standpoint since the implementation is not-thread safe except in this > specific usage contex [1] http://article.gmane.org/gmane.comp.version-control.git/196042 -- Duy -- To unsubscribe from this list: send the line "unsubscribe git" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
Re: Make the git codebase thread-safe
Even if we make that change to use TLS for this case, the implementation of pread() will still change in such a way that the semantics of pread() are different on Windows. Is that ok? Just to summarize, here's the viable approaches I've seen discussed so far: 1) Use _WINVER at compile time to select either a thread-safe or non-thread-safe implementation of pread. This is the easiest possible code change, but would necessitate 2 binary distributions of git for windows. 2) Use TLS as you suggest and have one fd per pack thread. Probably the most complicated code change (at least for me, being a first-time contributor) 3) Use Karsten's suggested implementation from earlier in the thread. Seems to work, but it's a little confusing from a readability standpoint since the implementation is not-thread safe except in this specific usage context. On Fri, Feb 14, 2014 at 4:56 PM, Duy Nguyen wrote: > On Sat, Feb 15, 2014 at 7:50 AM, Stefan Zager wrote: >> On Fri, Feb 14, 2014 at 4:45 PM, Duy Nguyen wrote: >>> On Sat, Feb 15, 2014 at 2:16 AM, Zachary Turner >>> wrote: (Gah, sorry if you're receiving multiple emails to your personal addresses, I need to get used to manually setting Plain-text mode every time I send a message). For the mixed read, we wouldn't be looking for another caller of pread() (since it doesn't care what the file pointer is), but instead a caller of read() or lseek() (since those do depend on the current file pointer). In index-pack.c, I see two possible culprits: 1) A call to xread() from inside fill() 2) A call to lseek in parse_pack_objects() Do you think these could be related? If so, maybe that opens up some other solutions? >>> >>> For index-pack alone, what's wrong with open one file handle per thread? >> >> Nothing wrong with that, except that it would mean either using >> thread-local storage (which the code doesn't currently use); or >> plumbing pack_fd through the call stack, which doesn't sound very fun. > > Current code does use thread-local storage (struct thread_local and > get_thread_data). Adding a new file handle when NO_THREAD_SAFE_PREAD > is defined is simpler imo. > -- > Duy -- To unsubscribe from this list: send the line "unsubscribe git" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
Re: Make the git codebase thread-safe
On Sat, Feb 15, 2014 at 7:50 AM, Stefan Zager wrote: > On Fri, Feb 14, 2014 at 4:45 PM, Duy Nguyen wrote: >> On Sat, Feb 15, 2014 at 2:16 AM, Zachary Turner wrote: >>> (Gah, sorry if you're receiving multiple emails to your personal >>> addresses, I need to get used to manually setting Plain-text mode >>> every time I send a message). >>> >>> For the mixed read, we wouldn't be looking for another caller of >>> pread() (since it doesn't care what the file pointer is), but instead >>> a caller of read() or lseek() (since those do depend on the current >>> file pointer). In index-pack.c, I see two possible culprits: >>> >>> 1) A call to xread() from inside fill() >>> 2) A call to lseek in parse_pack_objects() >>> >>> Do you think these could be related? If so, maybe that opens up some >>> other solutions? >> >> For index-pack alone, what's wrong with open one file handle per thread? > > Nothing wrong with that, except that it would mean either using > thread-local storage (which the code doesn't currently use); or > plumbing pack_fd through the call stack, which doesn't sound very fun. Current code does use thread-local storage (struct thread_local and get_thread_data). Adding a new file handle when NO_THREAD_SAFE_PREAD is defined is simpler imo. -- Duy -- To unsubscribe from this list: send the line "unsubscribe git" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
Re: Make the git codebase thread-safe
On Fri, Feb 14, 2014 at 4:45 PM, Duy Nguyen wrote: > On Sat, Feb 15, 2014 at 2:16 AM, Zachary Turner wrote: >> (Gah, sorry if you're receiving multiple emails to your personal >> addresses, I need to get used to manually setting Plain-text mode >> every time I send a message). >> >> For the mixed read, we wouldn't be looking for another caller of >> pread() (since it doesn't care what the file pointer is), but instead >> a caller of read() or lseek() (since those do depend on the current >> file pointer). In index-pack.c, I see two possible culprits: >> >> 1) A call to xread() from inside fill() >> 2) A call to lseek in parse_pack_objects() >> >> Do you think these could be related? If so, maybe that opens up some >> other solutions? > > For index-pack alone, what's wrong with open one file handle per thread? Nothing wrong with that, except that it would mean either using thread-local storage (which the code doesn't currently use); or plumbing pack_fd through the call stack, which doesn't sound very fun. Stefan > -- > Duy -- To unsubscribe from this list: send the line "unsubscribe git" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
Re: Make the git codebase thread-safe
On Sat, Feb 15, 2014 at 2:16 AM, Zachary Turner wrote: > (Gah, sorry if you're receiving multiple emails to your personal > addresses, I need to get used to manually setting Plain-text mode > every time I send a message). > > For the mixed read, we wouldn't be looking for another caller of > pread() (since it doesn't care what the file pointer is), but instead > a caller of read() or lseek() (since those do depend on the current > file pointer). In index-pack.c, I see two possible culprits: > > 1) A call to xread() from inside fill() > 2) A call to lseek in parse_pack_objects() > > Do you think these could be related? If so, maybe that opens up some > other solutions? For index-pack alone, what's wrong with open one file handle per thread? -- Duy -- To unsubscribe from this list: send the line "unsubscribe git" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
Re: Make the git codebase thread-safe
Am 14.02.2014 20:16, schrieb Zachary Turner:
> For the mixed read, we wouldn't be looking for another caller of
> pread() (since it doesn't care what the file pointer is), but instead
> a caller of read() or lseek() (since those do depend on the current
> file pointer). In index-pack.c, I see two possible culprits:
>
> 1) A call to xread() from inside fill()
> 2) A call to lseek in parse_pack_objects()
>
> Do you think these could be related? If so, maybe that opens up some
> other solutions?
>
Yeah, I think that's it. The problem is that the single-threaded part
(parse_pack_objects/parse_pack_header) _also_ calls pread (via sha1_object ->
get_data_from_pack -> unpack_data). So a pread() that modifies the file
position would naturally be bad in this single-threaded scenario. Incidentally,
that's exactly what the lstat64 in the version below fixes (similar to
git_pread).
> BTW, the version you posted isn't thread safe.
It is true that, in a multi-threaded scenario, my version modifies the file
position in some indeterministic way. However, as you noted above, the file
position is irrelevant to pread(), so that's perfectly thread-safe, as long as
all threads use pread() exclusively.
Using [x]read() in one of the threads would _not_ be thread-safe, but we're not
doing that here. Both fill()/xread() and parse_pack_objects()/lseek() are
unreachable from threaded_second_pass(), and the main thread just waits for the
background threads to complete...
>>> A simple alternative to ReOpenHandle is to reset the file pointer to its
>>> original position, as in compat/pread.c::git_pread. Thus single-theaded code
>>> can mix read()/pread() at will, but multi-threaded code has to use pread()
>>> exclusively (which is usually the case anyway). A main thread using read()
>>> and background threads using pread() (which is technically allowed by POSIX)
>>> will fail with this solution.
>>>
>>> This version passes the test suite on msysgit:
>>>
>>> 8<
>>> ssize_t mingw_pread(int fd, void *buf, size_t count, off64_t offset)
>>> {
>>> DWORD bytes_read;
>>> OVERLAPPED overlapped;
>>> off64_t current;
>>> memset(&overlapped, 0, sizeof(overlapped));
>>> overlapped.Offset = (DWORD) offset;
>>> overlapped.OffsetHigh = (DWORD) (offset >> 32);
>>>
>>> current = lseek64(fd, 0, SEEK_CUR);
>>>
>>> if (!ReadFile((HANDLE)_get_osfhandle(fd), buf, count, &bytes_read,
>>> &overlapped)) {
>>> errno = err_win_to_posix(GetLastError());
>>> return -1;
>>> }
>>>
>>> lseek64(fd, current, SEEK_SET);
>>>
>>> return (ssize_t) bytes_read;
>>> }
>>>
>>
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Re: Make the git codebase thread-safe
On Fri, Feb 14, 2014 at 11:04 AM, Karsten Blees wrote: > > Damn...you're right, multi-threaded git-index-pack works fine, but some tests > fail badly. Mixed reads would have to be from git_mmap, which is the only > other caller of pread(). msysgit used git_mmap() as defined in compat/win32mmap.c, which does not use pread. Stefan -- To unsubscribe from this list: send the line "unsubscribe git" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
Re: Make the git codebase thread-safe
On Fri, Feb 14, 2014 at 11:15 AM, Zachary Turner wrote: > For the mixed read, we wouldn't be looking for another caller of pread() > (since it doesn't care what the file pointer is), but instead a caller of > read() or lseek(). In index-pack.c, I see two possible culprits: > > 1) A call to xread() from inside fill() > 2) A call to lseek in parse_pack_objects() > > Do you think these could be related? If so, maybe that opens up some other > solutions? >From my observations, it's not that simple. As you pointed out to me before, fill() is only called before the threading part of the code, and lseek is only called after the threading part; and the lseek() is lseek(fd, 0, SEEK_CUR), so it's purely advisory. Also, here is the error output we got before you added ReOpenFile: remote: Total 2514467 (delta 1997300), reused 2513040 (delta 1997113) Checking connectivity... error: packfile d:/src/chromium2/_gclient_src_a6y1bf/.git/objects/pack/pack-3b8d06040ac37f14d0b43859926f1153fea61a7a.pack does not match index warning: packfile d:/src/chromium2/_gclient_src_a6y1bf/.git/objects/pack/pack-3b8d06040ac37f14d0b43859926f1153fea61a7a.pack cannot be accessed error: packfile d:/src/chromium2/_gclient_src_a6y1bf/.git/objects/pack/pack-3b8d06040ac37f14d0b43859926f1153fea61a7a.pack does not match index warning: packfile d:/src/chromium2/_gclient_src_a6y1bf/.git/objects/pack/pack-3b8d06040ac37f14d0b43859926f1153fea61a7a.pack cannot be accessed error: packfile d:/src/chromium2/_gclient_src_a6y1bf/.git/objects/pack/pack-3b8d06040ac37f14d0b43859926f1153fea61a7a.pack does not match index warning: packfile d:/src/chromium2/_gclient_src_a6y1bf/.git/objects/pack/pack-3b8d06040ac37f14d0b43859926f1153fea61a7a.pack cannot be accessed fatal: bad object e0f9f23f765a45e6d80863a8f881ee735c9347fe The 'Checking connectivity...' message comes from builtin/clone.c, which runs in a separate process from builtin/index-pack.c. What this suggests to me is that file descriptors for the loose object files are not being flushed or closed properly before index-pack finishes. > BTW, the version you posted isn't thread safe. Suppose thread A and thread > B execute this function at the same time. A executes through the > ReadFile(), but does not yet reset the second lseek64. B then executes the > first lseek64(), storing off the modified file pointer. Then A finishes, > then B finishes. At the end, the file pointer is still modified. Yes, that. I would also point out that in our experiments, ReOpenFile is not nearly as expensive as its name might suggest. Since the solution using ReOpenFile is pretty solidly thread-safe (at least as far as we can tell), I'm in favor of using it unless or until we properly root-case the failure. Stefan -- To unsubscribe from this list: send the line "unsubscribe git" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
Re: Make the git codebase thread-safe
(Gah, sorry if you're receiving multiple emails to your personal
addresses, I need to get used to manually setting Plain-text mode
every time I send a message).
For the mixed read, we wouldn't be looking for another caller of
pread() (since it doesn't care what the file pointer is), but instead
a caller of read() or lseek() (since those do depend on the current
file pointer). In index-pack.c, I see two possible culprits:
1) A call to xread() from inside fill()
2) A call to lseek in parse_pack_objects()
Do you think these could be related? If so, maybe that opens up some
other solutions?
BTW, the version you posted isn't thread safe. Suppose thread A and
thread B execute this function at the same time. A executes through
the ReadFile(), but does not yet reset the second lseek64. B then
executes the first lseek64(), storing off the modified file pointer.
Then A finishes, then B finishes. At the end, the file pointer is
still modified.
On Fri, Feb 14, 2014 at 11:15 AM, Zachary Turner wrote:
> For the mixed read, we wouldn't be looking for another caller of pread()
> (since it doesn't care what the file pointer is), but instead a caller of
> read() or lseek(). In index-pack.c, I see two possible culprits:
>
> 1) A call to xread() from inside fill()
> 2) A call to lseek in parse_pack_objects()
>
> Do you think these could be related? If so, maybe that opens up some other
> solutions?
>
> BTW, the version you posted isn't thread safe. Suppose thread A and thread
> B execute this function at the same time. A executes through the
> ReadFile(), but does not yet reset the second lseek64. B then executes the
> first lseek64(), storing off the modified file pointer. Then A finishes,
> then B finishes. At the end, the file pointer is still modified.
>
>
>
> On Fri, Feb 14, 2014 at 11:04 AM, Karsten Blees
> wrote:
>>
>> Am 14.02.2014 00:09, schrieb Zachary Turner:
>> > To elaborate a little bit more, you can verify with a sample program
>> > that ReadFile with OVERLAPPED does in fact modify the HANDLE's file
>> > position. The documentation doesn't actually state one way or
>> > another. My original attempt at a patch didn't have the ReOpenFile,
>> > and we experienced regular read corruption. We scratched our heads
>> > over it for a bit, and then hypothesized that someone must be mixing
>> > read styles, which led to this ReOpenFile workaround, which
>> > incidentally also solved the corruption problems. We wrote a similar
>> > sample program to verify that when using ReOpenHandle, and changing
>> > the file pointer of the duplicated handle, that the file pointer of
>> > the original handle is not modified.
>> >
>> > We did not actually try to identify the source of the mixed read
>> > styles, but it seems like the only possible explanation.
>> >
>> > On Thu, Feb 13, 2014 at 2:53 PM, Stefan Zager wrote:
>> >> On Thu, Feb 13, 2014 at 2:51 PM, Karsten Blees
>> >> wrote:
>> >>> Am 13.02.2014 19:38, schrieb Zachary Turner:
>> >>>
>> The only reason ReOpenFile is necessary at
>> all is because some code somewhere is mixing read-styles against the
>> same
>> fd.
>>
>> >>>
>> >>> I don't understand...ReadFile with OVERLAPPED parameter doesn't modify
>> >>> the HANDLE's file position, so you should be able to mix read()/pread()
>> >>> however you like (as long as read() is only called from one thread).
>> >>
>> >> That is, apparently, a bald-faced lie in the ReadFile API doc. First
>> >> implementation didn't use ReOpenFile, and it crashed all over the
>> >> place. ReOpenFile fixed it.
>> >>
>> >> Stefan
>>
>> Damn...you're right, multi-threaded git-index-pack works fine, but some
>> tests fail badly. Mixed reads would have to be from git_mmap, which is the
>> only other caller of pread().
>>
>> A simple alternative to ReOpenHandle is to reset the file pointer to its
>> original position, as in compat/pread.c::git_pread. Thus single-theaded code
>> can mix read()/pread() at will, but multi-threaded code has to use pread()
>> exclusively (which is usually the case anyway). A main thread using read()
>> and background threads using pread() (which is technically allowed by POSIX)
>> will fail with this solution.
>>
>> This version passes the test suite on msysgit:
>>
>> 8<
>> ssize_t mingw_pread(int fd, void *buf, size_t count, off64_t offset)
>> {
>> DWORD bytes_read;
>> OVERLAPPED overlapped;
>> off64_t current;
>> memset(&overlapped, 0, sizeof(overlapped));
>> overlapped.Offset = (DWORD) offset;
>> overlapped.OffsetHigh = (DWORD) (offset >> 32);
>>
>> current = lseek64(fd, 0, SEEK_CUR);
>>
>> if (!ReadFile((HANDLE)_get_osfhandle(fd), buf, count, &bytes_read,
>> &overlapped)) {
>> errno = err_win_to_posix(GetLastError());
>> return -1;
>> }
>>
>> lseek64(fd, current, SEEK_SET);
>>
>> return (ssize_t) bytes_read;
>> }
>>
>
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To unsubscribe from thi
Re: Make the git codebase thread-safe
Am 14.02.2014 00:09, schrieb Zachary Turner:
> To elaborate a little bit more, you can verify with a sample program
> that ReadFile with OVERLAPPED does in fact modify the HANDLE's file
> position. The documentation doesn't actually state one way or
> another. My original attempt at a patch didn't have the ReOpenFile,
> and we experienced regular read corruption. We scratched our heads
> over it for a bit, and then hypothesized that someone must be mixing
> read styles, which led to this ReOpenFile workaround, which
> incidentally also solved the corruption problems. We wrote a similar
> sample program to verify that when using ReOpenHandle, and changing
> the file pointer of the duplicated handle, that the file pointer of
> the original handle is not modified.
>
> We did not actually try to identify the source of the mixed read
> styles, but it seems like the only possible explanation.
>
> On Thu, Feb 13, 2014 at 2:53 PM, Stefan Zager wrote:
>> On Thu, Feb 13, 2014 at 2:51 PM, Karsten Blees
>> wrote:
>>> Am 13.02.2014 19:38, schrieb Zachary Turner:
>>>
The only reason ReOpenFile is necessary at
all is because some code somewhere is mixing read-styles against the same
fd.
>>>
>>> I don't understand...ReadFile with OVERLAPPED parameter doesn't modify the
>>> HANDLE's file position, so you should be able to mix read()/pread() however
>>> you like (as long as read() is only called from one thread).
>>
>> That is, apparently, a bald-faced lie in the ReadFile API doc. First
>> implementation didn't use ReOpenFile, and it crashed all over the
>> place. ReOpenFile fixed it.
>>
>> Stefan
Damn...you're right, multi-threaded git-index-pack works fine, but some tests
fail badly. Mixed reads would have to be from git_mmap, which is the only other
caller of pread().
A simple alternative to ReOpenHandle is to reset the file pointer to its
original position, as in compat/pread.c::git_pread. Thus single-theaded code
can mix read()/pread() at will, but multi-threaded code has to use pread()
exclusively (which is usually the case anyway). A main thread using read() and
background threads using pread() (which is technically allowed by POSIX) will
fail with this solution.
This version passes the test suite on msysgit:
8<
ssize_t mingw_pread(int fd, void *buf, size_t count, off64_t offset)
{
DWORD bytes_read;
OVERLAPPED overlapped;
off64_t current;
memset(&overlapped, 0, sizeof(overlapped));
overlapped.Offset = (DWORD) offset;
overlapped.OffsetHigh = (DWORD) (offset >> 32);
current = lseek64(fd, 0, SEEK_CUR);
if (!ReadFile((HANDLE)_get_osfhandle(fd), buf, count, &bytes_read,
&overlapped)) {
errno = err_win_to_posix(GetLastError());
return -1;
}
lseek64(fd, current, SEEK_SET);
return (ssize_t) bytes_read;
}
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Re: Make the git codebase thread-safe
To elaborate a little bit more, you can verify with a sample program that ReadFile with OVERLAPPED does in fact modify the HANDLE's file position. The documentation doesn't actually state one way or another. My original attempt at a patch didn't have the ReOpenFile, and we experienced regular read corruption. We scratched our heads over it for a bit, and then hypothesized that someone must be mixing read styles, which led to this ReOpenFile workaround, which incidentally also solved the corruption problems. We wrote a similar sample program to verify that when using ReOpenHandle, and changing the file pointer of the duplicated handle, that the file pointer of the original handle is not modified. We did not actually try to identify the source of the mixed read styles, but it seems like the only possible explanation. On Thu, Feb 13, 2014 at 2:53 PM, Stefan Zager wrote: > On Thu, Feb 13, 2014 at 2:51 PM, Karsten Blees > wrote: >> Am 13.02.2014 19:38, schrieb Zachary Turner: >> >>> The only reason ReOpenFile is necessary at >>> all is because some code somewhere is mixing read-styles against the same >>> fd. >>> >> >> I don't understand...ReadFile with OVERLAPPED parameter doesn't modify the >> HANDLE's file position, so you should be able to mix read()/pread() however >> you like (as long as read() is only called from one thread). > > That is, apparently, a bald-faced lie in the ReadFile API doc. First > implementation didn't use ReOpenFile, and it crashed all over the > place. ReOpenFile fixed it. > > Stefan -- To unsubscribe from this list: send the line "unsubscribe git" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
Re: Make the git codebase thread-safe
On Thu, Feb 13, 2014 at 2:51 PM, Karsten Blees wrote: > Am 13.02.2014 19:38, schrieb Zachary Turner: > >> The only reason ReOpenFile is necessary at >> all is because some code somewhere is mixing read-styles against the same >> fd. >> > > I don't understand...ReadFile with OVERLAPPED parameter doesn't modify the > HANDLE's file position, so you should be able to mix read()/pread() however > you like (as long as read() is only called from one thread). That is, apparently, a bald-faced lie in the ReadFile API doc. First implementation didn't use ReOpenFile, and it crashed all over the place. ReOpenFile fixed it. Stefan -- To unsubscribe from this list: send the line "unsubscribe git" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
Re: Make the git codebase thread-safe
Am 13.02.2014 19:38, schrieb Zachary Turner:
> The only reason ReOpenFile is necessary at
> all is because some code somewhere is mixing read-styles against the same
> fd.
>
I don't understand...ReadFile with OVERLAPPED parameter doesn't modify the
HANDLE's file position, so you should be able to mix read()/pread() however you
like (as long as read() is only called from one thread).
I tried without ReOpenFile and it seems to work like a charm, or am I missing
something?
8<
ssize_t mingw_pread(int fd, void *buf, size_t count, off64_t offset)
{
DWORD bytes_read;
OVERLAPPED overlapped;
memset(&overlapped, 0, sizeof(overlapped));
overlapped.Offset = (DWORD) offset;
overlapped.OffsetHigh = (DWORD) (offset >> 32);
if (!ReadFile((HANDLE) _get_osfhandle(fd), buf, count, &bytes_read,
&overlapped)) {
errno = err_win_to_posix(GetLastError());
return -1;
}
return (ssize_t) bytes_read;
}
--
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Re: Make the git codebase thread-safe
Karsten Blees gmail.com> writes: > > Am 12.02.2014 19:37, schrieb Erik Faye-Lund: > > On Wed, Feb 12, 2014 at 7:34 PM, Stefan Zager google.com> wrote: > >> On Wed, Feb 12, 2014 at 10:27 AM, Erik Faye-Lund gmail.com> wrote: > >>> On Wed, Feb 12, 2014 at 7:20 PM, Stefan Zager google.com> wrote: > > I don't want to steal the thunder of my coworker, who wrote the > implementation. He plans to submit it upstream soon-ish. It relies > on using the lpOverlapped argument to ReadFile(), with some additional > tomfoolery to make sure that the implicit position pointer for the > file descriptor doesn't get modified. > >>> > >>> Is the code available somewhere? I'm especially interested in the > >>> "additional tomfoolery to make sure that the implicit position pointer > >>> for the file descriptor doesn't get modified"-part, as this was what I > >>> ended up butting my head into when trying to do this myself. > >> > >> https://chromium-review.googlesource.com/#/c/186104/ > > > > ReOpenFile, that's fantastic. Thanks a lot! > > ...but should be loaded dynamically via GetProcAddress, or are we ready to drop XP support? > > Original patch author here. In trying to prepare this patch to use GetProcAddress to load dynamically, I've run into a bit of a snag. NO_THREAD_SAFE_PREAD is a compile-time flag, which will be incompatible with any attempt to make this a runtime decision a la LoadLibrary / GetProcAddress. On XP, we would need to fallback to the single-threaded path, and on Vista+ we would use the thread-able path, and obviously this decision could not be made until runtime. If MinGW were the only configuration using NO_THREAD_SAFE_PREAD, I would just remove it entirely, but it appears Cygwin configuration uses it also. Suggestions? One possibility is to disallow (by convention, perhaps), the use of pread() and read() against the same fd. The only reason ReOpenFile is necessary at all is because some code somewhere is mixing read-styles against the same fd. -- To unsubscribe from this list: send the line "unsubscribe git" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
Re: Make the git codebase thread-safe
On Thu, Feb 13, 2014 at 12:27 AM, Johannes Sixt wrote: > Am 2/12/2014 20:30, schrieb Stefan Zager: >> On Wed, Feb 12, 2014 at 11:22 AM, Karsten Blees >> wrote: >>> Am 12.02.2014 19:37, schrieb Erik Faye-Lund: ReOpenFile, that's fantastic. Thanks a lot! >>> >>> ...but should be loaded dynamically via GetProcAddress, or are we ready to >>> drop XP support? >> >> Right, that is an issue. From our perspective, it's well past time to >> drop XP support. > > Not from mine. All this really means is that the build config will test WIN_VER, and there will need to be an additional binary distribution of msysgit for newer Windows. -- To unsubscribe from this list: send the line "unsubscribe git" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
Re: Make the git codebase thread-safe
On Thu, Feb 13, 2014 at 06:34:39PM +0900, Mike Hommey wrote: > On Thu, Feb 13, 2014 at 07:04:02AM +0100, David Kastrup wrote: > > Mike Hommey writes: > > > > > On Wed, Feb 12, 2014 at 08:15:24PM +0100, David Kastrup wrote: > > >> Stefan Zager writes: > > >> > > >> > On Wed, Feb 12, 2014 at 10:50 AM, David Kastrup wrote: > > >> > > > >> >> Really, give the above patch a try. I am taking longer to finish it > > >> >> than anticipated (with a lot due to procrastination but that is, > > >> >> unfortunately, a large part of my workflow), and it's cutting into my > > >> >> "paychecks" (voluntary donations which to a good degree depend on > > >> >> timely > > >> >> and nontrivial progress reports for my freely available work on GNU > > >> >> LilyPond). > > >> > > > >> > I will give that a try. How much of a performance improvement have > > >> > you clocked? > > >> > > >> Depends on file type and size. With large files with lots of small > > >> changes, performance improvements get more impressive. > > >> > > >> Some ugly real-world examples are the Emacs repository, src/xdisp.c > > >> (performance improvement about a factor of 3), a large file in the style > > >> of /usr/share/dict/words clocking in at a factor of about 5. > > >> > > >> Again, that's with an SSD and ext4 filesystem on GNU/Linux, and there > > >> are no improvements in system time (I/O) except for patch 4 of the > > >> series which helps perhaps 20% or so. > > >> > > >> So the benefits of the patch will come into play mostly for big, bad > > >> files on Windows: other than that, the I/O time is likely to be the > > >> dominant player anyway. > > > > > > How much fragmentation does that add to the files, though? > > > > Uh, git-blame is a read-only operation. It does not add fragmentation > > to any file. The patch will add a diff of probably a few dozen hunks to > > builtin/blame.c. Do you call that "fragmentation"? It is small enough > > that I expect even > > > > git blame builtin/blame.c > > > > to be faster than before. But that interpretation of your question > > probably tries to make too much sense out of what is just nonsense in > > the given context. > > Sorry, I thought you were talking about write operations, not reads. Specifically, I thought you were talking about git checkout. Mike -- To unsubscribe from this list: send the line "unsubscribe git" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
Re: Make the git codebase thread-safe
On Thu, Feb 13, 2014 at 07:04:02AM +0100, David Kastrup wrote: > Mike Hommey writes: > > > On Wed, Feb 12, 2014 at 08:15:24PM +0100, David Kastrup wrote: > >> Stefan Zager writes: > >> > >> > On Wed, Feb 12, 2014 at 10:50 AM, David Kastrup wrote: > >> > > >> >> Really, give the above patch a try. I am taking longer to finish it > >> >> than anticipated (with a lot due to procrastination but that is, > >> >> unfortunately, a large part of my workflow), and it's cutting into my > >> >> "paychecks" (voluntary donations which to a good degree depend on timely > >> >> and nontrivial progress reports for my freely available work on GNU > >> >> LilyPond). > >> > > >> > I will give that a try. How much of a performance improvement have > >> > you clocked? > >> > >> Depends on file type and size. With large files with lots of small > >> changes, performance improvements get more impressive. > >> > >> Some ugly real-world examples are the Emacs repository, src/xdisp.c > >> (performance improvement about a factor of 3), a large file in the style > >> of /usr/share/dict/words clocking in at a factor of about 5. > >> > >> Again, that's with an SSD and ext4 filesystem on GNU/Linux, and there > >> are no improvements in system time (I/O) except for patch 4 of the > >> series which helps perhaps 20% or so. > >> > >> So the benefits of the patch will come into play mostly for big, bad > >> files on Windows: other than that, the I/O time is likely to be the > >> dominant player anyway. > > > > How much fragmentation does that add to the files, though? > > Uh, git-blame is a read-only operation. It does not add fragmentation > to any file. The patch will add a diff of probably a few dozen hunks to > builtin/blame.c. Do you call that "fragmentation"? It is small enough > that I expect even > > git blame builtin/blame.c > > to be faster than before. But that interpretation of your question > probably tries to make too much sense out of what is just nonsense in > the given context. Sorry, I thought you were talking about write operations, not reads. Mike -- To unsubscribe from this list: send the line "unsubscribe git" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
Re: Make the git codebase thread-safe
Johannes Sixt writes: > Am 2/12/2014 20:30, schrieb Stefan Zager: >> On Wed, Feb 12, 2014 at 11:22 AM, Karsten Blees >> wrote: >>> Am 12.02.2014 19:37, schrieb Erik Faye-Lund: ReOpenFile, that's fantastic. Thanks a lot! >>> >>> ...but should be loaded dynamically via GetProcAddress, or are we >>> ready to drop XP support? >> >> Right, that is an issue. From our perspective, it's well past time to >> drop XP support. > > Not from mine. XP has not even reached end of life yet. As a point of comparison, there are tensions on the Emacs developer list several times a decade because some people suggest it might be time to drop the MSDOS port and/or the associated restriction of having filenames be unique in the 8+3 naming scheme. -- David Kastrup -- To unsubscribe from this list: send the line "unsubscribe git" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
Re: Make the git codebase thread-safe
David Kastrup writes: > Again, that's with an SSD and ext4 filesystem on GNU/Linux, and there > are no improvements in system time (I/O) except for patch 4 of the > series which helps perhaps 20% or so. > > So the benefits of the patch will come into play mostly for big, bad > files on Windows: other than that, the I/O time is likely to be the > dominant player anyway. > > If you have benchmarked the stuff, for annoying cases expect I/O time > to go down maybe 10-20%, and user time to drop by a factor of 4. > Under GNU/Linux, that makes for a significant overall improvement. On > Windows, the payback is likely quite less because of the worse I/O > performance. Pity. But of course, you can significantly reduce the relevant file open/close/search times by running git gc --aggressive While this does not actually help with performance in GNU/Linux (though with file space), dealing with few but compressed files under Windows is likely a reasonably big win since the uncompression happens in user space and cannot be bungled by Microsoft (apart from bad memory management strategies). -- David Kastrup -- To unsubscribe from this list: send the line "unsubscribe git" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
Re: Make the git codebase thread-safe
Mike Hommey writes: > On Wed, Feb 12, 2014 at 08:15:24PM +0100, David Kastrup wrote: >> Stefan Zager writes: >> >> > On Wed, Feb 12, 2014 at 10:50 AM, David Kastrup wrote: >> > >> >> Really, give the above patch a try. I am taking longer to finish it >> >> than anticipated (with a lot due to procrastination but that is, >> >> unfortunately, a large part of my workflow), and it's cutting into my >> >> "paychecks" (voluntary donations which to a good degree depend on timely >> >> and nontrivial progress reports for my freely available work on GNU >> >> LilyPond). >> > >> > I will give that a try. How much of a performance improvement have >> > you clocked? >> >> Depends on file type and size. With large files with lots of small >> changes, performance improvements get more impressive. >> >> Some ugly real-world examples are the Emacs repository, src/xdisp.c >> (performance improvement about a factor of 3), a large file in the style >> of /usr/share/dict/words clocking in at a factor of about 5. >> >> Again, that's with an SSD and ext4 filesystem on GNU/Linux, and there >> are no improvements in system time (I/O) except for patch 4 of the >> series which helps perhaps 20% or so. >> >> So the benefits of the patch will come into play mostly for big, bad >> files on Windows: other than that, the I/O time is likely to be the >> dominant player anyway. > > How much fragmentation does that add to the files, though? Uh, git-blame is a read-only operation. It does not add fragmentation to any file. The patch will add a diff of probably a few dozen hunks to builtin/blame.c. Do you call that "fragmentation"? It is small enough that I expect even git blame builtin/blame.c to be faster than before. But that interpretation of your question probably tries to make too much sense out of what is just nonsense in the given context. -- David Kastrup -- To unsubscribe from this list: send the line "unsubscribe git" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
Re: Make the git codebase thread-safe
Am 2/12/2014 20:30, schrieb Stefan Zager: > On Wed, Feb 12, 2014 at 11:22 AM, Karsten Blees > wrote: >> Am 12.02.2014 19:37, schrieb Erik Faye-Lund: >>> ReOpenFile, that's fantastic. Thanks a lot! >> >> ...but should be loaded dynamically via GetProcAddress, or are we ready to >> drop XP support? > > Right, that is an issue. From our perspective, it's well past time to > drop XP support. Not from mine. -- Hannes -- To unsubscribe from this list: send the line "unsubscribe git" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
Re: Make the git codebase thread-safe
On Tue, Feb 11, 2014 at 05:54:51PM -0800, Stefan Zager wrote: > To this end, I'd like to start submitting patches that make the code > base generally more thread-safe and thread-friendly. Right after this > email, I'm going to send the first such patch, which makes the global > list of pack files (packed_git) internal to sha1_file.c. I'm definitely interested in this if it also works on POSIX systems. At work, we have a 7.6 GiB repo (packed)[0], so while performance is not bad, I certainly wouldn't object if it were better. [0] Using du -sh. For comparison, the Linux kernel repo is 1.4 GiB. -- brian m. carlson / brian with sandals: Houston, Texas, US +1 832 623 2791 | http://www.crustytoothpaste.net/~bmc | My opinion only OpenPGP: RSA v4 4096b: 88AC E9B2 9196 305B A994 7552 F1BA 225C 0223 B187 signature.asc Description: Digital signature
Re: Make the git codebase thread-safe
Am 13.02.2014 00:03, schrieb Mike Hommey: > On Wed, Feb 12, 2014 at 12:00:19PM +0100, Karsten Blees wrote: >> Am 12.02.2014 04:43, schrieb Duy Nguyen: >>> On Wed, Feb 12, 2014 at 9:02 AM, Robin H. Johnson >>> wrote: On Tue, Feb 11, 2014 at 05:54:51PM -0800, Stefan Zager wrote: > We in the chromium project have a keen interest in adding threading to > git in the pursuit of performance for lengthy operations (checkout, > status, blame, ...). Our motivation comes from hitting some > performance walls when working with repositories the size of chromium > and blink: +1 from Gentoo on performance improvements for large repos. The main repository in the ongoing Git migration project looks to be in the 1.5GB range (and for those that want to propose splitting it up, we have explored that option and found it lacking), with very deep history (but no branches of note, and very few tags). >>> >>> From v1.9 shallow clone should work for all push/pull/clone... so >>> history depth does not matter (on the client side). As for >>> gentoo-x86's large worktree, using index v4 and avoid full-tree >>> operations (e.g. "status .", not "status"..) should make all >>> operations reasonably fast. I plan to make "status" fast even without >>> path limiting with the help of inotify, but that's not going to be >>> finished soon. Did I miss anything else? >>> >> >> Regarding git-status on msysgit, enable core.preloadindex and core.fscache >> (as of 1.8.5.2). >> >> There's no inotify on Windows, and I gave up using ReadDirectoryChangesW to >> keep fscache up to date, as it _may_ report DOS file names (e.g. C:\PROGRA~1 >> instead of C:\Program Files). > > You can use GetLongPathNameW to get the latter from the former. > > Mike > Except if its a delete or rename notification...my final ReadDirectoryChangesW version cached the files by their long _and_ short names, but was so complex that it slowed most commands down rather than speeding them up :-) -- To unsubscribe from this list: send the line "unsubscribe git" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
Re: Make the git codebase thread-safe
On Wed, Feb 12, 2014 at 12:00:19PM +0100, Karsten Blees wrote: > Am 12.02.2014 04:43, schrieb Duy Nguyen: > > On Wed, Feb 12, 2014 at 9:02 AM, Robin H. Johnson > > wrote: > >> On Tue, Feb 11, 2014 at 05:54:51PM -0800, Stefan Zager wrote: > >>> We in the chromium project have a keen interest in adding threading to > >>> git in the pursuit of performance for lengthy operations (checkout, > >>> status, blame, ...). Our motivation comes from hitting some > >>> performance walls when working with repositories the size of chromium > >>> and blink: > >> +1 from Gentoo on performance improvements for large repos. > >> > >> The main repository in the ongoing Git migration project looks to be in > >> the 1.5GB range (and for those that want to propose splitting it up, we > >> have explored that option and found it lacking), with very deep history > >> (but no branches of note, and very few tags). > > > > From v1.9 shallow clone should work for all push/pull/clone... so > > history depth does not matter (on the client side). As for > > gentoo-x86's large worktree, using index v4 and avoid full-tree > > operations (e.g. "status .", not "status"..) should make all > > operations reasonably fast. I plan to make "status" fast even without > > path limiting with the help of inotify, but that's not going to be > > finished soon. Did I miss anything else? > > > > Regarding git-status on msysgit, enable core.preloadindex and core.fscache > (as of 1.8.5.2). > > There's no inotify on Windows, and I gave up using ReadDirectoryChangesW to > keep fscache up to date, as it _may_ report DOS file names (e.g. C:\PROGRA~1 > instead of C:\Program Files). You can use GetLongPathNameW to get the latter from the former. Mike -- To unsubscribe from this list: send the line "unsubscribe git" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
Re: Make the git codebase thread-safe
On Wed, Feb 12, 2014 at 08:15:24PM +0100, David Kastrup wrote: > Stefan Zager writes: > > > On Wed, Feb 12, 2014 at 10:50 AM, David Kastrup wrote: > > > >> Really, give the above patch a try. I am taking longer to finish it > >> than anticipated (with a lot due to procrastination but that is, > >> unfortunately, a large part of my workflow), and it's cutting into my > >> "paychecks" (voluntary donations which to a good degree depend on timely > >> and nontrivial progress reports for my freely available work on GNU > >> LilyPond). > > > > I will give that a try. How much of a performance improvement have > > you clocked? > > Depends on file type and size. With large files with lots of small > changes, performance improvements get more impressive. > > Some ugly real-world examples are the Emacs repository, src/xdisp.c > (performance improvement about a factor of 3), a large file in the style > of /usr/share/dict/words clocking in at a factor of about 5. > > Again, that's with an SSD and ext4 filesystem on GNU/Linux, and there > are no improvements in system time (I/O) except for patch 4 of the > series which helps perhaps 20% or so. > > So the benefits of the patch will come into play mostly for big, bad > files on Windows: other than that, the I/O time is likely to be the > dominant player anyway. How much fragmentation does that add to the files, though? Mike -- To unsubscribe from this list: send the line "unsubscribe git" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
Re: Make the git codebase thread-safe
On Wed, Feb 12, 2014 at 12:27 PM, Stefan Zager wrote: > On Wed, Feb 12, 2014 at 12:06 PM, Junio C Hamano wrote: >> Stefan Zager writes: >> >> Calls to write (and preparation of data to be written) will then >> remain single-threaded, but it sounds like that codepath is not the >> bottleneck in your measurement, so > > Yes, I considered that as well. At a minimum, that would still > require attr.c to implement thread locking, since attribute files must > be parsed to look for stream filters. I have already done that work. I would have imagined that use of the attribute system belongs to "write and preparation of data to be written" category, i.e. the single threaded part of the kludge I outlined. > But I'm not sure it's the best long-term approach to add convoluted > custom threading solutions to each git operation as it appears on the > performance radar. Yeah, it depends on how clean and non-intrusive an abstraction we can make. The kludge I outlined is certainly not very pretty. -- To unsubscribe from this list: send the line "unsubscribe git" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
Re: Make the git codebase thread-safe
On Wed, Feb 12, 2014 at 12:06 PM, Junio C Hamano wrote: > Stefan Zager writes: > >> ... I used the Very Sleepy profiler >> to see where all the time was spent on Windows: 55% of the time was >> spent in OpenFile, and 25% in CloseFile (both in win32). > > This is somewhat interesting. > > When we check things out, checkout_paths() has a list of paths to be > checked out, and iterates over them and call checkout_entry(). > > I wonder if you can: > > - introduce a version of checkout_entry() that takes file >descriptors to write to; > > - have an asynchronous helper threads that pre-open the paths to be >written out and feed to a >queue; > > - restructure that loop so that it reads the to be written> from the queue, performs the actual writing out, >and then feeds to another queue; and > > - have another asynchronous helper threads that reads descriptor to be closed> from the queue and close them. > > Calls to write (and preparation of data to be written) will then > remain single-threaded, but it sounds like that codepath is not the > bottleneck in your measurement, so Yes, I considered that as well. At a minimum, that would still require attr.c to implement thread locking, since attribute files must be parsed to look for stream filters. I have already done that work. But I'm not sure it's the best long-term approach to add convoluted custom threading solutions to each git operation as it appears on the performance radar. I'm hoping to make the entire code base more thread-friendly, so that threading can be added in a more natural and idiomatic (and less painful) way. For example, the most natural way to add threading to checkout would be in the loops over the index in check_updates() in unpack-trees.c. If attr.c and sha1_file.c were thread-safe, then it would be possible to thread checkout entirely in check_updates(), with a pretty compact code change. I have already done the work in attr.c; sha1_file.c is hairier, but do-able. Stefan -- To unsubscribe from this list: send the line "unsubscribe git" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
Re: Make the git codebase thread-safe
Stefan Zager writes: > ... I used the Very Sleepy profiler > to see where all the time was spent on Windows: 55% of the time was > spent in OpenFile, and 25% in CloseFile (both in win32). This is somewhat interesting. When we check things out, checkout_paths() has a list of paths to be checked out, and iterates over them and call checkout_entry(). I wonder if you can: - introduce a version of checkout_entry() that takes file descriptors to write to; - have an asynchronous helper threads that pre-open the paths to be written out and feed to a queue; - restructure that loop so that it reads the from the queue, performs the actual writing out, and then feeds to another queue; and - have another asynchronous helper threads that reads from the queue and close them. Calls to write (and preparation of data to be written) will then remain single-threaded, but it sounds like that codepath is not the bottleneck in your measurement, so -- To unsubscribe from this list: send the line "unsubscribe git" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
Re: Make the git codebase thread-safe
On Wed, Feb 12, 2014 at 11:22 AM, Karsten Blees wrote: > Am 12.02.2014 19:37, schrieb Erik Faye-Lund: >> On Wed, Feb 12, 2014 at 7:34 PM, Stefan Zager wrote: >>> On Wed, Feb 12, 2014 at 10:27 AM, Erik Faye-Lund >>> wrote: On Wed, Feb 12, 2014 at 7:20 PM, Stefan Zager wrote: > > I don't want to steal the thunder of my coworker, who wrote the > implementation. He plans to submit it upstream soon-ish. It relies > on using the lpOverlapped argument to ReadFile(), with some additional > tomfoolery to make sure that the implicit position pointer for the > file descriptor doesn't get modified. Is the code available somewhere? I'm especially interested in the "additional tomfoolery to make sure that the implicit position pointer for the file descriptor doesn't get modified"-part, as this was what I ended up butting my head into when trying to do this myself. >>> >>> https://chromium-review.googlesource.com/#/c/186104/ >> >> ReOpenFile, that's fantastic. Thanks a lot! > > ...but should be loaded dynamically via GetProcAddress, or are we ready to > drop XP support? Right, that is an issue. From our perspective, it's well past time to drop XP support. -- To unsubscribe from this list: send the line "unsubscribe git" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
Re: Make the git codebase thread-safe
Am 12.02.2014 19:37, schrieb Erik Faye-Lund: > On Wed, Feb 12, 2014 at 7:34 PM, Stefan Zager wrote: >> On Wed, Feb 12, 2014 at 10:27 AM, Erik Faye-Lund wrote: >>> On Wed, Feb 12, 2014 at 7:20 PM, Stefan Zager wrote: I don't want to steal the thunder of my coworker, who wrote the implementation. He plans to submit it upstream soon-ish. It relies on using the lpOverlapped argument to ReadFile(), with some additional tomfoolery to make sure that the implicit position pointer for the file descriptor doesn't get modified. >>> >>> Is the code available somewhere? I'm especially interested in the >>> "additional tomfoolery to make sure that the implicit position pointer >>> for the file descriptor doesn't get modified"-part, as this was what I >>> ended up butting my head into when trying to do this myself. >> >> https://chromium-review.googlesource.com/#/c/186104/ > > ReOpenFile, that's fantastic. Thanks a lot! ...but should be loaded dynamically via GetProcAddress, or are we ready to drop XP support? -- To unsubscribe from this list: send the line "unsubscribe git" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
Re: Make the git codebase thread-safe
Stefan Zager writes: > On Wed, Feb 12, 2014 at 10:50 AM, David Kastrup wrote: > >> Really, give the above patch a try. I am taking longer to finish it >> than anticipated (with a lot due to procrastination but that is, >> unfortunately, a large part of my workflow), and it's cutting into my >> "paychecks" (voluntary donations which to a good degree depend on timely >> and nontrivial progress reports for my freely available work on GNU >> LilyPond). > > I will give that a try. How much of a performance improvement have > you clocked? Depends on file type and size. With large files with lots of small changes, performance improvements get more impressive. Some ugly real-world examples are the Emacs repository, src/xdisp.c (performance improvement about a factor of 3), a large file in the style of /usr/share/dict/words clocking in at a factor of about 5. Again, that's with an SSD and ext4 filesystem on GNU/Linux, and there are no improvements in system time (I/O) except for patch 4 of the series which helps perhaps 20% or so. So the benefits of the patch will come into play mostly for big, bad files on Windows: other than that, the I/O time is likely to be the dominant player anyway. If you have benchmarked the stuff, for annoying cases expect I/O time to go down maybe 10-20%, and user time to drop by a factor of 4. Under GNU/Linux, that makes for a significant overall improvement. On Windows, the payback is likely quite less because of the worse I/O performance. Pity. -- David Kastrup -- To unsubscribe from this list: send the line "unsubscribe git" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
Re: Make the git codebase thread-safe
On Wed, Feb 12, 2014 at 10:50 AM, David Kastrup wrote: > Stefan Zager writes: > >> Anything on Windows that touches a lot of files is miserable due to >> the usual file system slowness on Windows, and luafv.sys (the UAC file >> virtualization driver) seems to make it much worse. > > There is an obvious solution here... Dedicated hardware is not that > expensive. Virtualization will always have a price. Not sure I follow you. We need to support people developing, building, and testing on natively Windows machines. And we need to support users with reasonable hardware, including spinning disks. If we were only interested in optimizing for Google employees, each of whom has one or more small nuclear reactors under their desk, this would be easy. >> Blame is something that chromium and blink developers use heavily, and >> it is not unusual for a blame invocation on the blink repository to >> run for 30 seconds. It seems like it should be possible to >> parallelize blame, but it requires pack file operations to be >> thread-safe. > > Really, give the above patch a try. I am taking longer to finish it > than anticipated (with a lot due to procrastination but that is, > unfortunately, a large part of my workflow), and it's cutting into my > "paychecks" (voluntary donations which to a good degree depend on timely > and nontrivial progress reports for my freely available work on GNU > LilyPond). I will give that a try. How much of a performance improvement have you clocked? > Note that it looks like the majority of the remaining time on GNU/Linux > tends to be spent in system time: I/O time, memory management. And I > have an SSD drive. When using packed repositories of considerable size, > decompression comes into play as well. I don't think that you can hope > to get noticeably higher I/O throughput by multithreading, so really, > really, really consider dedicated hardware running on a native Linux > file system. I have a background in hardware, and I have much more faith in modern disk schedulers :) Stefan -- To unsubscribe from this list: send the line "unsubscribe git" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
Re: Make the git codebase thread-safe
Stefan Zager writes: > On Tue, Feb 11, 2014 at 6:11 PM, Duy Nguyen wrote: >> >> I have no comments about thread safety improvements (well, not yet). >> If you have investigated about git performance on chromium >> repositories, could you please sum it up? Threading may be an option >> to improve performance, but it's probably not the only option. > > Well, the painful operations that we use frequently are pack-objects, > checkout, status, and blame. Have you checked the patch in http://thread.gmane.org/gmane.comp.version-control.git/241448> and followups, Message-ID: <1391454849-26558-1-git-send-email-...@gnu.org>? While this does not yet support -M and -C options, it's conceivable that you don't use them in your server/scripts. > Anything on Windows that touches a lot of files is miserable due to > the usual file system slowness on Windows, and luafv.sys (the UAC file > virtualization driver) seems to make it much worse. There is an obvious solution here... Dedicated hardware is not that expensive. Virtualization will always have a price. > Blame is something that chromium and blink developers use heavily, and > it is not unusual for a blame invocation on the blink repository to > run for 30 seconds. It seems like it should be possible to > parallelize blame, but it requires pack file operations to be > thread-safe. Really, give the above patch a try. I am taking longer to finish it than anticipated (with a lot due to procrastination but that is, unfortunately, a large part of my workflow), and it's cutting into my "paychecks" (voluntary donations which to a good degree depend on timely and nontrivial progress reports for my freely available work on GNU LilyPond). Note that it looks like the majority of the remaining time on GNU/Linux tends to be spent in system time: I/O time, memory management. And I have an SSD drive. When using packed repositories of considerable size, decompression comes into play as well. I don't think that you can hope to get noticeably higher I/O throughput by multithreading, so really, really, really consider dedicated hardware running on a native Linux file system. -- David Kastrup -- To unsubscribe from this list: send the line "unsubscribe git" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
Re: Make the git codebase thread-safe
On Wed, Feb 12, 2014 at 7:34 PM, Stefan Zager wrote: > On Wed, Feb 12, 2014 at 10:27 AM, Erik Faye-Lund wrote: >> On Wed, Feb 12, 2014 at 7:20 PM, Stefan Zager wrote: >>> >>> I don't want to steal the thunder of my coworker, who wrote the >>> implementation. He plans to submit it upstream soon-ish. It relies >>> on using the lpOverlapped argument to ReadFile(), with some additional >>> tomfoolery to make sure that the implicit position pointer for the >>> file descriptor doesn't get modified. >> >> Is the code available somewhere? I'm especially interested in the >> "additional tomfoolery to make sure that the implicit position pointer >> for the file descriptor doesn't get modified"-part, as this was what I >> ended up butting my head into when trying to do this myself. > > https://chromium-review.googlesource.com/#/c/186104/ ReOpenFile, that's fantastic. Thanks a lot! -- To unsubscribe from this list: send the line "unsubscribe git" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
Re: Make the git codebase thread-safe
On Wed, Feb 12, 2014 at 10:33 AM, Matthieu Moy wrote: > Stefan Zager writes: > >> I'm optimistic that parallelizing the stat calls will yield a further >> improvement. > > It has already been mentionned in the thread, but in case you overlooked > it: did you look at core.preloadindex? It seems at least very close to > what you want. Ah yes, sorry, I overlooked that. We have indeed turned on core.preloadindex, and it does indeed speed up status. That speedup is reflected in my previous comments about our observations working with chromium and blink. Stefan -- To unsubscribe from this list: send the line "unsubscribe git" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
Re: Make the git codebase thread-safe
On Wed, Feb 12, 2014 at 10:27 AM, Erik Faye-Lund wrote: > On Wed, Feb 12, 2014 at 7:20 PM, Stefan Zager wrote: >> >> I don't want to steal the thunder of my coworker, who wrote the >> implementation. He plans to submit it upstream soon-ish. It relies >> on using the lpOverlapped argument to ReadFile(), with some additional >> tomfoolery to make sure that the implicit position pointer for the >> file descriptor doesn't get modified. > > Is the code available somewhere? I'm especially interested in the > "additional tomfoolery to make sure that the implicit position pointer > for the file descriptor doesn't get modified"-part, as this was what I > ended up butting my head into when trying to do this myself. https://chromium-review.googlesource.com/#/c/186104/ -- To unsubscribe from this list: send the line "unsubscribe git" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
Re: Make the git codebase thread-safe
Stefan Zager writes: > I'm optimistic that parallelizing the stat calls will yield a further > improvement. It has already been mentionned in the thread, but in case you overlooked it: did you look at core.preloadindex? It seems at least very close to what you want. -- Matthieu Moy http://www-verimag.imag.fr/~moy/ -- To unsubscribe from this list: send the line "unsubscribe git" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
Re: Make the git codebase thread-safe
On Wed, Feb 12, 2014 at 7:20 PM, Stefan Zager wrote: > On Wed, Feb 12, 2014 at 3:59 AM, Erik Faye-Lund wrote: >> On Wed, Feb 12, 2014 at 2:54 AM, Stefan Zager wrote: >>> >>> We are particularly concerned with the performance of msysgit, and we >>> have already chalked up a significant performance gain by turning on >>> the threading code in pack-objects (which was already enabled for >>> posix platforms, but not on msysgit, owing to the lack of a correct >>> pread implementation). >> >> How did you manage to do this? I'm not aware of any way to implement >> pread on Windows (without going down the insanity-path of wrapping and >> potentially locking inside every IO operation)... > > I don't want to steal the thunder of my coworker, who wrote the > implementation. He plans to submit it upstream soon-ish. It relies > on using the lpOverlapped argument to ReadFile(), with some additional > tomfoolery to make sure that the implicit position pointer for the > file descriptor doesn't get modified. Is the code available somewhere? I'm especially interested in the "additional tomfoolery to make sure that the implicit position pointer for the file descriptor doesn't get modified"-part, as this was what I ended up butting my head into when trying to do this myself. -- To unsubscribe from this list: send the line "unsubscribe git" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
Re: Make the git codebase thread-safe
On Wed, Feb 12, 2014 at 3:59 AM, Erik Faye-Lund wrote: > On Wed, Feb 12, 2014 at 2:54 AM, Stefan Zager wrote: >> >> We are particularly concerned with the performance of msysgit, and we >> have already chalked up a significant performance gain by turning on >> the threading code in pack-objects (which was already enabled for >> posix platforms, but not on msysgit, owing to the lack of a correct >> pread implementation). > > How did you manage to do this? I'm not aware of any way to implement > pread on Windows (without going down the insanity-path of wrapping and > potentially locking inside every IO operation)... I don't want to steal the thunder of my coworker, who wrote the implementation. He plans to submit it upstream soon-ish. It relies on using the lpOverlapped argument to ReadFile(), with some additional tomfoolery to make sure that the implicit position pointer for the file descriptor doesn't get modified. Stefan -- To unsubscribe from this list: send the line "unsubscribe git" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
Re: Make the git codebase thread-safe
On Tue, Feb 11, 2014 at 7:43 PM, Duy Nguyen wrote: > > From v1.9 shallow clone should work for all push/pull/clone... so > history depth does not matter (on the client side). As for > gentoo-x86's large worktree, using index v4 and avoid full-tree > operations (e.g. "status .", not "status"..) should make all > operations reasonably fast. I plan to make "status" fast even without > path limiting with the help of inotify, but that's not going to be > finished soon. Did I miss anything else? Chromium developers frequently want to run status over their entire checkout, and a lot of them run 'git commit -a'. We want to do everything possible to speed this up. -- To unsubscribe from this list: send the line "unsubscribe git" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
Re: Make the git codebase thread-safe
On Tue, Feb 11, 2014 at 6:11 PM, Duy Nguyen wrote: > > I have no comments about thread safety improvements (well, not yet). > If you have investigated about git performance on chromium > repositories, could you please sum it up? Threading may be an option > to improve performance, but it's probably not the only option. Well, the painful operations that we use frequently are pack-objects, checkout, status, and blame. Anything on Windows that touches a lot of files is miserable due to the usual file system slowness on Windows, and luafv.sys (the UAC file virtualization driver) seems to make it much worse. With threading turned on, pack-objects on Windows now takes about twice as long as on Linux, which is still more than a 2x improvement over the non-threaded operation. Checkout is really bad on Windows. The blink repository is ~200K files, and a full clean checkout from the index takes about 10 seconds on Linux, and about 3:30 on Windows. I used the Very Sleepy profiler to see where all the time was spent on Windows: 55% of the time was spent in OpenFile, and 25% in CloseFile (both in win32). My immediate goal is to add threading to checkout, so those file system calls can be done in parallel. Enabling the fscache speeds up status quite a bit. I'm optimistic that parallelizing the stat calls will yield a further improvement. Beyond that, it may not be possible to do much more without using a file system watcher daemon, like facebook does with mercurial. (https://code.facebook.com/posts/218678814984400/scaling-mercurial-at-facebook/) Blame is something that chromium and blink developers use heavily, and it is not unusual for a blame invocation on the blink repository to run for 30 seconds. It seems like it should be possible to parallelize blame, but it requires pack file operations to be thread-safe. Stefan -- To unsubscribe from this list: send the line "unsubscribe git" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
Re: Make the git codebase thread-safe
On Wed, Feb 12, 2014 at 2:54 AM, Stefan Zager wrote: > We in the chromium project have a keen interest in adding threading to > git in the pursuit of performance for lengthy operations (checkout, > status, blame, ...). Our motivation comes from hitting some > performance walls when working with repositories the size of chromium > and blink: > > https://chromium.googlesource.com/chromium/src > https://chromium.googlesource.com/chromium/blink > > We are particularly concerned with the performance of msysgit, and we > have already chalked up a significant performance gain by turning on > the threading code in pack-objects (which was already enabled for > posix platforms, but not on msysgit, owing to the lack of a correct > pread implementation). How did you manage to do this? I'm not aware of any way to implement pread on Windows (without going down the insanity-path of wrapping and potentially locking inside every IO operation)... -- To unsubscribe from this list: send the line "unsubscribe git" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
Re: Make the git codebase thread-safe
Am 12.02.2014 04:43, schrieb Duy Nguyen: > On Wed, Feb 12, 2014 at 9:02 AM, Robin H. Johnson wrote: >> On Tue, Feb 11, 2014 at 05:54:51PM -0800, Stefan Zager wrote: >>> We in the chromium project have a keen interest in adding threading to >>> git in the pursuit of performance for lengthy operations (checkout, >>> status, blame, ...). Our motivation comes from hitting some >>> performance walls when working with repositories the size of chromium >>> and blink: >> +1 from Gentoo on performance improvements for large repos. >> >> The main repository in the ongoing Git migration project looks to be in >> the 1.5GB range (and for those that want to propose splitting it up, we >> have explored that option and found it lacking), with very deep history >> (but no branches of note, and very few tags). > > From v1.9 shallow clone should work for all push/pull/clone... so > history depth does not matter (on the client side). As for > gentoo-x86's large worktree, using index v4 and avoid full-tree > operations (e.g. "status .", not "status"..) should make all > operations reasonably fast. I plan to make "status" fast even without > path limiting with the help of inotify, but that's not going to be > finished soon. Did I miss anything else? > Regarding git-status on msysgit, enable core.preloadindex and core.fscache (as of 1.8.5.2). There's no inotify on Windows, and I gave up using ReadDirectoryChangesW to keep fscache up to date, as it _may_ report DOS file names (e.g. C:\PROGRA~1 instead of C:\Program Files). -- To unsubscribe from this list: send the line "unsubscribe git" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
Re: Make the git codebase thread-safe
On Wed, Feb 12, 2014 at 9:02 AM, Robin H. Johnson wrote: > On Tue, Feb 11, 2014 at 05:54:51PM -0800, Stefan Zager wrote: >> We in the chromium project have a keen interest in adding threading to >> git in the pursuit of performance for lengthy operations (checkout, >> status, blame, ...). Our motivation comes from hitting some >> performance walls when working with repositories the size of chromium >> and blink: > +1 from Gentoo on performance improvements for large repos. > > The main repository in the ongoing Git migration project looks to be in > the 1.5GB range (and for those that want to propose splitting it up, we > have explored that option and found it lacking), with very deep history > (but no branches of note, and very few tags). >From v1.9 shallow clone should work for all push/pull/clone... so history depth does not matter (on the client side). As for gentoo-x86's large worktree, using index v4 and avoid full-tree operations (e.g. "status .", not "status"..) should make all operations reasonably fast. I plan to make "status" fast even without path limiting with the help of inotify, but that's not going to be finished soon. Did I miss anything else? -- Duy -- To unsubscribe from this list: send the line "unsubscribe git" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
Re: Make the git codebase thread-safe
On Wed, Feb 12, 2014 at 8:54 AM, Stefan Zager wrote: > We in the chromium project have a keen interest in adding threading to > git in the pursuit of performance for lengthy operations (checkout, > status, blame, ...). Our motivation comes from hitting some > performance walls when working with repositories the size of chromium > and blink: > > https://chromium.googlesource.com/chromium/src > https://chromium.googlesource.com/chromium/blink I have no comments about thread safety improvements (well, not yet). If you have investigated about git performance on chromium repositories, could you please sum it up? Threading may be an option to improve performance, but it's probably not the only option. -- Duy -- To unsubscribe from this list: send the line "unsubscribe git" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
Re: Make the git codebase thread-safe
On Tue, Feb 11, 2014 at 05:54:51PM -0800, Stefan Zager wrote: > We in the chromium project have a keen interest in adding threading to > git in the pursuit of performance for lengthy operations (checkout, > status, blame, ...). Our motivation comes from hitting some > performance walls when working with repositories the size of chromium > and blink: +1 from Gentoo on performance improvements for large repos. The main repository in the ongoing Git migration project looks to be in the 1.5GB range (and for those that want to propose splitting it up, we have explored that option and found it lacking), with very deep history (but no branches of note, and very few tags). -- Robin Hugh Johnson Gentoo Linux: Developer, Infrastructure Lead E-Mail : robb...@gentoo.org GnuPG FP : 11ACBA4F 4778E3F6 E4EDF38E B27B944E 34884E85 -- To unsubscribe from this list: send the line "unsubscribe git" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
