| Message ID | f572e226bb5e4b67cc57f8d9d4732086f01190a2.1603143316.git.gitgitgadget@gmail.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | use fsmonitor data in git diff eliminating O(num_files) calls to lstat | expand |
On Mon, Oct 19, 2020 at 09:35:15PM +0000, Nipunn Koorapati via GitGitGadget wrote: > diff --git a/t/perf/p7519-fsmonitor.sh b/t/perf/p7519-fsmonitor.sh > index 9313d4a51d..2b4803707f 100755 > --- a/t/perf/p7519-fsmonitor.sh > +++ b/t/perf/p7519-fsmonitor.sh > @@ -115,6 +115,13 @@ test_expect_success "setup for fsmonitor" ' > > git config core.fsmonitor "$INTEGRATION_SCRIPT" && > git update-index --fsmonitor && > + mkdir 1_file 10_files 100_files 1000_files 10000_files && > + for i in `seq 1 10`; do touch 10_files/$i; done && > + for i in `seq 1 100`; do touch 100_files/$i; done && > + for i in `seq 1 1000`; do touch 1000_files/$i; done && > + for i in `seq 1 10000`; do touch 10000_files/$i; done && I just happened to notice these while reading your range diff; git discourages the use of seq in test, instead preferring our own works-everywhere 'test_seq()'. I was wondering how this slipped through since it should be checked automatically by t/check-non-portable-shell.pl, but that is only run from t/Makefile, not t/perf/Makefile. That probably explains how a few raw `seq`'s made it into t/perf. In either case, test_seq() is preferred here. Thanks, Taylor
On Mon, Oct 19, 2020 at 09:35:15PM +0000, Nipunn Koorapati via GitGitGadget wrote: > From: Nipunn Koorapati <nipunn@dropbox.com> > > Results for the git-diff fsmonitor optimization > in patch in the parent-rev (using a 400k file repo to test) > > As you can see here - git diff with fsmonitor running is > significantly better with this patch series (80% faster on my > workload)! These t/perf numbers are very helpful, at least to me. > GIT_PERF_LARGE_REPO=~/src/server ./run v2.29.0-rc1 . -- p7519-fsmonitor.sh > > Test v2.29.0-rc1 this tree > ----------------------------------------------------------------------------------------------------------------- > 7519.2: status (fsmonitor=.git/hooks/fsmonitor-watchman) 1.46(0.82+0.64) 1.47(0.83+0.62) +0.7% > 7519.3: status -uno (fsmonitor=.git/hooks/fsmonitor-watchman) 0.16(0.12+0.04) 0.17(0.12+0.05) +6.3% > 7519.4: status -uall (fsmonitor=.git/hooks/fsmonitor-watchman) 1.36(0.73+0.62) 1.37(0.76+0.60) +0.7% Looks like about 0.01sec of overhead, which seems like an acceptable trade-off for when the user has at least 10,000 files. This reminds me; did you look at the 'git add' performance change? I recall Junio mentioning that 'git add' takes the same paths in the code. > 7519.5: diff (fsmonitor=.git/hooks/fsmonitor-watchman) 0.85(0.22+0.63) 0.14(0.10+0.05) -83.5% > 7519.6: diff -- 0_files (fsmonitor=.git/hooks/fsmonitor-watchman) 0.12(0.08+0.05) 0.13(0.11+0.02) +8.3% > 7519.7: diff -- 10_files (fsmonitor=.git/hooks/fsmonitor-watchman) 0.12(0.08+0.04) 0.13(0.09+0.04) +8.3% > 7519.8: diff -- 100_files (fsmonitor=.git/hooks/fsmonitor-watchman) 0.12(0.07+0.05) 0.13(0.07+0.06) +8.3% > 7519.9: diff -- 1000_files (fsmonitor=.git/hooks/fsmonitor-watchman) 0.12(0.09+0.04) 0.13(0.08+0.05) +8.3% > 7519.10: diff -- 10000_files (fsmonitor=.git/hooks/fsmonitor-watchman) 0.14(0.09+0.05) 0.13(0.10+0.03) -7.1% OK... so having fsmonitor turned on adds an imperceptible amount of slow-down to cases where there are [0, 10000) files. But, in exchange, you get much-improved whole-tree performance, as well as single-tree performance when that tree contains at least 10,000 files. I was going to say that this has little downside, because turning on fsmonitor is probably a good indicator that you don't have any fewer than 10,000 files in your repository, but I think that's missing the point. Likely true, but that doesn't exclude the possibility of having sub-10,000 file directories, which users may very well still be diff-ing. So, there's a slow-down, but it's hard to complain when you consider what we get in exchange. > 7519.12: status (fsmonitor=) 1.67(0.93+1.49) 1.67(0.99+1.42) +0.0% > 7519.13: status -uno (fsmonitor=) 0.37(0.30+0.82) 0.37(0.33+0.79) +0.0% > 7519.14: status -uall (fsmonitor=) 1.58(0.97+1.35) 1.57(0.86+1.45) -0.6% > 7519.15: diff (fsmonitor=) 0.34(0.28+0.83) 0.34(0.27+0.83) +0.0% > 7519.16: diff -- 0_files (fsmonitor=) 0.09(0.06+0.04) 0.09(0.08+0.02) +0.0% > 7519.17: diff -- 10_files (fsmonitor=) 0.09(0.07+0.03) 0.09(0.06+0.05) +0.0% > 7519.18: diff -- 100_files (fsmonitor=) 0.09(0.06+0.04) 0.09(0.06+0.04) +0.0% > 7519.19: diff -- 1000_files (fsmonitor=) 0.09(0.06+0.04) 0.09(0.05+0.05) +0.0% > 7519.20: diff -- 10000_files (fsmonitor=) 0.10(0.08+0.04) 0.10(0.06+0.05) +0.0% Great! No slow-down without fsmonitor enabled, as expected. Fantastic. > I also added a benchmark for a tiny git diff workload w/ a pathspec. > I see an approximately .02 second overhead added w/ and w/o fsmonitor > > From looking at these results, I suspected that refresh_fsmonitor > is already happening during git diff - independent of this patch > series' optimization. Confirmed that suspicion by breaking on > refresh_fsmonitor. So, the overhead that we're paying is purely the pipe+fork+exec? I.e., that watchman has already computed an answer in the earlier call, and we just have to read it again (or find out that the last results were unchanged)? > (gdb) bt [simplified] > 0 refresh_fsmonitor at fsmonitor.c:176 > 1 ie_match_stat at read-cache.c:375 > 2 match_stat_with_submodule at diff-lib.c:237 > 4 builtin_diff_files at builtin/diff.c:260 > 5 cmd_diff at builtin/diff.c:541 > 6 run_builtin at git.c:450 > 7 handle_builtin at git.c:700 > 8 run_argv at git.c:767 > 9 cmd_main at git.c:898 > 10 main at common-main.c:52 :-). > Signed-off-by: Nipunn Koorapati <nipunn@dropbox.com> > --- > t/perf/p7519-fsmonitor.sh | 71 +++++++++++++++++++++++++++++++++++++++ > 1 file changed, 71 insertions(+) > > diff --git a/t/perf/p7519-fsmonitor.sh b/t/perf/p7519-fsmonitor.sh > index 9313d4a51d..2b4803707f 100755 > --- a/t/perf/p7519-fsmonitor.sh > +++ b/t/perf/p7519-fsmonitor.sh > @@ -115,6 +115,13 @@ test_expect_success "setup for fsmonitor" ' Everything in here looks very reasonable to me, except for the seq vs. test_seq() issue that I pointed out in another email in this thread. It's too bad that we have to write these twice, but that's not the fault of your patch. Thanks, Taylor
> I was wondering how this slipped through since it should be checked > automatically by t/check-non-portable-shell.pl, but that is only run > from t/Makefile, not t/perf/Makefile. That probably explains how a few > raw `seq`'s made it into t/perf. Makefile issue is easy enough to fix - will fix in another commit
On Mon, Oct 19, 2020 at 11:00:05PM +0100, Nipunn Koorapati wrote: > > I was wondering how this slipped through since it should be checked > > automatically by t/check-non-portable-shell.pl, but that is only run > > from t/Makefile, not t/perf/Makefile. That probably explains how a few > > raw `seq`'s made it into t/perf. > > Makefile issue is easy enough to fix - will fix in another commit Thanks; I don't think that you need to worry about touching up t/perf's Makefile (although I'd be very grateful if you did!), but rather just swapping new invocations of seq to use 'test_seq()' would be sufficient in and of itself. Thanks, Taylor
> This reminds me; did you look at the 'git add' performance change? I > recall Junio mentioning that 'git add' takes the same paths in the code. I did look into it and didn't see a big perf change - and didn't dig into why. I'll leave a perf test in the next roll of this patch series so you can see the numbers. --Nipunn
diff --git a/t/perf/p7519-fsmonitor.sh b/t/perf/p7519-fsmonitor.sh index 9313d4a51d..2b4803707f 100755 --- a/t/perf/p7519-fsmonitor.sh +++ b/t/perf/p7519-fsmonitor.sh @@ -115,6 +115,13 @@ test_expect_success "setup for fsmonitor" ' git config core.fsmonitor "$INTEGRATION_SCRIPT" && git update-index --fsmonitor && + mkdir 1_file 10_files 100_files 1000_files 10000_files && + for i in `seq 1 10`; do touch 10_files/$i; done && + for i in `seq 1 100`; do touch 100_files/$i; done && + for i in `seq 1 1000`; do touch 1000_files/$i; done && + for i in `seq 1 10000`; do touch 10000_files/$i; done && + git add 1_file 10_files 100_files 1000_files 10000_files && + git commit -m "Add files" && git status # Warm caches ' @@ -142,6 +149,38 @@ test_perf "status -uall (fsmonitor=$INTEGRATION_SCRIPT)" ' git status -uall ' +if test -n "$GIT_PERF_7519_DROP_CACHE"; then + test-tool drop-caches +fi + +test_perf "diff (fsmonitor=$INTEGRATION_SCRIPT)" ' + git diff +' + +if test -n "$GIT_PERF_7519_DROP_CACHE"; then + test-tool drop-caches +fi + +test_perf "diff -- 0_files (fsmonitor=$INTEGRATION_SCRIPT)" ' + git diff -- 1_file +' + +test_perf "diff -- 10_files (fsmonitor=$INTEGRATION_SCRIPT)" ' + git diff -- 10_files +' + +test_perf "diff -- 100_files (fsmonitor=$INTEGRATION_SCRIPT)" ' + git diff -- 100_files +' + +test_perf "diff -- 1000_files (fsmonitor=$INTEGRATION_SCRIPT)" ' + git diff -- 1000_files +' + +test_perf "diff -- 10000_files (fsmonitor=$INTEGRATION_SCRIPT)" ' + git diff -- 10000_files +' + test_expect_success "setup without fsmonitor" ' unset INTEGRATION_SCRIPT && git config --unset core.fsmonitor && @@ -172,6 +211,38 @@ test_perf "status -uall (fsmonitor=$INTEGRATION_SCRIPT)" ' git status -uall ' +if test -n "$GIT_PERF_7519_DROP_CACHE"; then + test-tool drop-caches +fi + +test_perf "diff (fsmonitor=$INTEGRATION_SCRIPT)" ' + git diff +' + +if test -n "$GIT_PERF_7519_DROP_CACHE"; then + test-tool drop-caches +fi + +test_perf "diff -- 0_files (fsmonitor=$INTEGRATION_SCRIPT)" ' + git diff -- 1_file +' + +test_perf "diff -- 10_files (fsmonitor=$INTEGRATION_SCRIPT)" ' + git diff -- 10_files +' + +test_perf "diff -- 100_files (fsmonitor=$INTEGRATION_SCRIPT)" ' + git diff -- 100_files +' + +test_perf "diff -- 1000_files (fsmonitor=$INTEGRATION_SCRIPT)" ' + git diff -- 1000_files +' + +test_perf "diff -- 10000_files (fsmonitor=$INTEGRATION_SCRIPT)" ' + git diff -- 10000_files +' + if test_have_prereq WATCHMAN then watchman watch-del "$GIT_WORK_TREE" >/dev/null 2>&1 &&