Jeff King <p...@peff.net> writes: > On Tue, Mar 18, 2014 at 12:50:50AM -0400, Jeff King wrote: > >> On Sun, Mar 16, 2014 at 08:35:04PM +0700, Nguyễn Thái Ngọc Duy wrote: >> >> > As explained in the previous commit, current aggressive settings >> > --depth=250 --window=250 could slow down repository access >> > significantly. Notice that people usually work on recent history only, >> > we could keep recent history more loosely packed, so that repo access >> > is fast most of the time while the pack file remains small. >> >> One thing I have not seen is real-world timings showing the slowdown >> based on --depth. Did I miss them, or are we just making assumptions >> based on one old case from 2009 (that, AFAIK does not have real numbers, >> just speculation)? Has anyone measured the effect of bumping the delta >> cache size (and its hash implementation)? > > Just as a very quick, rough data point, here are before-and-after > timings for the patch below doing "git rev-list --objects --all" on my > linux.git, which is a mix of "--aggressive" and normal packing (I didn't > do a "repack -f", but it's partially what I've downloaded from k.org and > what I've repacked in various experiments over the past few months). > > [before] > real 0m28.824s > user 0m28.620s > sys 0m0.232s > > [after] > real 0m21.694s > user 0m21.544s > sys 0m0.172s > > The numbers below are completely pulled out of a hat, so we can perhaps > do even better. But I think it shows that there is room for improvement > in the delta base cache. > > --- > diff --git a/environment.c b/environment.c > index c3c8606..73ed670 100644 > --- a/environment.c > +++ b/environment.c > @@ -37,7 +37,7 @@ int core_compression_seen; > int fsync_object_files; > size_t packed_git_window_size = DEFAULT_PACKED_GIT_WINDOW_SIZE; > size_t packed_git_limit = DEFAULT_PACKED_GIT_LIMIT; > -size_t delta_base_cache_limit = 16 * 1024 * 1024; > +size_t delta_base_cache_limit = 128 * 1024 * 1024;
You need to change a file in Documentation as well. Can offer a patch. > unsigned long big_file_threshold = 512 * 1024 * 1024; > const char *pager_program; > int pager_use_color = 1; > diff --git a/sha1_file.c b/sha1_file.c > index b37c6f6..a9ab8e3 100644 > --- a/sha1_file.c > +++ b/sha1_file.c > @@ -1944,7 +1944,7 @@ static void *unpack_compressed_entry(struct packed_git > *p, > return buffer; > } > > -#define MAX_DELTA_CACHE (256) > +#define MAX_DELTA_CACHE (1024) This one really needs experimentation. I found that increases here lead to performance degradation rather soon, probably because of decreased memory locality without significant reduction in cache collisions. Not sure whether it's worth touching at all. -- 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
