On Mon, May 21, 2012 at 07:52:19PM -0400, Jeff King wrote:
> Try doing "git fetch . refs/*:refs/*" in a repository with a large
> number of refs (e.g., 400K). With git v1.7.10, this takes about 9.5s on
> my machine. But using the version of git in "next" takes about 16.5s.
> Bisection points to your 432ad41 (refs: store references hierarchically,
> 2012-04-10). Perf shows sort_ref_dir and msort_with_tmp as hot spots.
A few more facts:
- I usually compile with -O0 because I am debugging so frequently.
With -O3, those numbers become 6.0s and 11.2s, respectively. Much
faster, but there is still a performance regression.
- Almost all of the refs are packed. IIRC, the packed-refs file should
already be sorted. I wonder if we did not bother double-checking
that before your patch, and now we do. That could explain the
difference.
- I don't compile with INTERNAL_QSORT. So mentioning msort_with_tmp is
slightly confusing, as it is actually the version from libc, not
ours IOW, it is really just qsort. But the primary culprit remains
sort_ref_dir.
-Peff
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