Re: [PATCH v2] sha1_file: use strbuf_add() instead of strbuf_addf()

[Derrick Stolee]

On 12/4/2017 11:56 AM, Jeff King wrote:

When you put your cover letter first, you need to use "scissors" like:
-- >8 --

to separate it from the commit message. Using three-dashes means "git
am" will include your cover letter as the commit message, and omit your
real commit message entirely.


Thanks. I updated our internal best-practices accordingly.

-Stolee

Re: [PATCH v2] sha1_file: use strbuf_add() instead of strbuf_addf()

[Jeff King]

On Mon, Dec 04, 2017 at 09:06:03AM -0500, Derrick Stolee wrote:

> Thanks for the feedback on v1. This version fixes the cruft_cb
> bug and streamlines the strlen(). I would include an inter-diff
> but it was the same size as the patch.

Thanks, this version looks good to me. One procedural nit:

> Thanks,
> -Stolee
> 
> ---

When you put your cover letter first, you need to use "scissors" like:

-- >8 --

to separate it from the commit message. Using three-dashes means "git
am" will include your cover letter as the commit message, and omit your
real commit message entirely.

-Peff

[PATCH v2] sha1_file: use strbuf_add() instead of strbuf_addf()

[Derrick Stolee]

Thanks for the feedback on v1. This version fixes the cruft_cb
bug and streamlines the strlen(). I would include an inter-diff
but it was the same size as the patch.

Thanks,
-Stolee

---

Replace use of strbuf_addf() with strbuf_add() when enumerating
loose objects in for_each_file_in_obj_subdir(). Since we already
check the length and hex-values of the string before consuming
the path, we can prevent extra computation by using the lower-
level method.

One consumer of for_each_file_in_obj_subdir() is the abbreviation
code. OID abbreviations use a cached list of loose objects (per
object subdirectory) to make repeated queries fast, but there is
significant cache load time when there are many loose objects.

Most repositories do not have many loose objects before repacking,
but in the GVFS case the repos can grow to have millions of loose
objects. Profiling 'git log' performance in GitForWindows on a
GVFS-enabled repo with ~2.5 million loose objects revealed 12% of
the CPU time was spent in strbuf_addf().

Add a new performance test to p4211-line-log.sh that is more
sensitive to this cache-loading. By limiting to 1000 commits, we
more closely resemble user wait time when reading history into a
pager.

For a copy of the Linux repo with two ~512 MB packfiles and ~572K
loose objects, running 'git log --oneline --parents --raw -1000'
had the following performance:

 HEAD~1HEAD

 7.70(7.15+0.54)   7.44(7.09+0.29) -3.4%

Signed-off-by: Derrick Stolee 
---
 sha1_file.c  | 12 +++-
 t/perf/p4211-line-log.sh |  4 
 2 files changed, 11 insertions(+), 5 deletions(-)

diff --git a/sha1_file.c b/sha1_file.c
index 8ae6cb6285..2fc8fa93b4 100644
--- a/sha1_file.c
+++ b/sha1_file.c
@@ -1903,7 +1903,6 @@ int for_each_file_in_obj_subdir(unsigned int subdir_nr,
origlen = path->len;
strbuf_complete(path, '/');
strbuf_addf(path, "%02x", subdir_nr);
-   baselen = path->len;
 
dir = opendir(path->buf);
if (!dir) {
@@ -1914,15 +1913,18 @@ int for_each_file_in_obj_subdir(unsigned int subdir_nr,
}
 
oid.hash[0] = subdir_nr;
+   strbuf_addch(path, '/');
+   baselen = path->len;
 
while ((de = readdir(dir))) {
+   size_t namelen;
if (is_dot_or_dotdot(de->d_name))
continue;
 
+   namelen = strlen(de->d_name);
strbuf_setlen(path, baselen);
-   strbuf_addf(path, "/%s", de->d_name);
-
-   if (strlen(de->d_name) == GIT_SHA1_HEXSZ - 2 &&
+   strbuf_add(path, de->d_name, namelen);
+   if (namelen == GIT_SHA1_HEXSZ - 2 &&
!hex_to_bytes(oid.hash + 1, de->d_name,
  GIT_SHA1_RAWSZ - 1)) {
if (obj_cb) {
@@ -1941,7 +1943,7 @@ int for_each_file_in_obj_subdir(unsigned int subdir_nr,
}
closedir(dir);
 
-   strbuf_setlen(path, baselen);
+   strbuf_setlen(path, baselen - 1);
if (!r && subdir_cb)
r = subdir_cb(subdir_nr, path->buf, data);
 
diff --git a/t/perf/p4211-line-log.sh b/t/perf/p4211-line-log.sh
index e0ed05907c..392bcc0e51 100755
--- a/t/perf/p4211-line-log.sh
+++ b/t/perf/p4211-line-log.sh
@@ -35,4 +35,8 @@ test_perf 'git log --oneline --raw --parents' '
git log --oneline --raw --parents >/dev/null
 '
 
+test_perf 'git log --oneline --raw --parents -1000' '
+   git log --oneline --raw --parents -1000 >/dev/null
+'
+
 test_done
-- 
2.15.0