Credit to alexmv who made this commit back in Dec, 2017 when he was at dbx. I've rebased it and am submitting it now. With fsmonitor enabled, git diff currently lstats every file in the repo This makes use of the fsmonitor extension to skip lstat() calls on files that fsmonitor judged as unmodified. I was able to do some testing with/without this change in a large in-house repo (~ 400k files) ----------------------------------------- (1) With fsmonitor enabled - on master of git (2.29.0) ----------------------------------------- ../git/bin-wrappers/git checkout HEAD~200 strace -c ../git/bin-wrappers/git diff % time seconds usecs/call calls errors syscall ------ ----------- ----------- --------- --------- ---------------- 99.64 4.358994 10 446257 3 lstat 0.12 0.005353 7 764 360 open (A subsequent call) strace -c ../git/bin-wrappers/git diff % time seconds usecs/call calls errors syscall ------ ----------- ----------- --------- --------- ---------------- 99.84 4.380955 10 444904 3 lstat 0.06 0.002564 135 19 munmap ... ----------------------------------------- (2) With fsmonitor enabled - with my patch ----------------------------------------- ../git/bin-wrappers/git checkout HEAD~200 strace -c ../git/bin-wrappers/git diff % time seconds usecs/call calls errors syscall ------ ----------- ----------- --------- --------- ---------------- 50.72 0.003090 163 19 munmap 19.63 0.001196 598 2 futex ... 0.00 0.000000 0 4 3 lstat ----------------------------------------- (3) With fsmonitor disabled entirely ----------------------------------------- % time seconds usecs/call calls errors syscall ------ ----------- ----------- --------- --------- ---------------- 98.52 0.277085 92362 3 futex 0.27 0.000752 4 191 63 open ... 0.14 0.000397 3 158 3 lstat I encoded this into a perf test with results as follow: On master (2.29) Test this tree -------------------------------------------------------------------------------- 7519.2: status (fsmonitor=.git/hooks/fsmonitor-watchman) 2.52(1.59+1.56) 7519.3: status -uno (fsmonitor=.git/hooks/fsmonitor-watchman) 0.18(0.12+0.06) 7519.4: status -uall (fsmonitor=.git/hooks/fsmonitor-watchman) 1.36(0.73+0.62) 7519.5: diff (fsmonitor=.git/hooks/fsmonitor-watchman) 0.85(0.30+0.54) 7519.7: status (fsmonitor=) 0.69(0.52+0.90) 7519.8: status -uno (fsmonitor=) 0.37(0.28+0.81) 7519.9: status -uall (fsmonitor=) 1.53(0.93+1.32) 7519.10: diff (fsmonitor=) 0.34(0.26+0.81) With this patch Test this tree -------------------------------------------------------------------------------- 7519.2: status (fsmonitor=.git/hooks/fsmonitor-watchman) 2.84(1.70+1.76) 7519.3: status -uno (fsmonitor=.git/hooks/fsmonitor-watchman) 0.18(0.13+0.05) 7519.4: status -uall (fsmonitor=.git/hooks/fsmonitor-watchman) 1.35(0.81+0.53) 7519.5: diff (fsmonitor=.git/hooks/fsmonitor-watchman) 0.15(0.11+0.05) 7519.7: status (fsmonitor=) 0.71(0.54+0.90) 7519.8: status -uno (fsmonitor=) 0.38(0.30+0.81) 7519.9: status -uall (fsmonitor=) 1.55(0.93+1.34) 7519.10: diff (fsmonitor=) 0.35(0.32+0.76) Alex Vandiver (1): fsmonitor: use fsmonitor data in `git diff` Nipunn Koorapati (3): t/perf/README: elaborate on output format t/perf/p7519-fsmonitor.sh: warm cache on first git status t/perf: add fsmonitor perf test for git diff diff-lib.c | 17 +++++++++++++++-- t/perf/README | 2 ++ t/perf/p7519-fsmonitor.sh | 19 ++++++++++++++++++- 3 files changed, 35 insertions(+), 3 deletions(-) base-commit: d4a392452e292ff924e79ec8458611c0f679d6d4 Published-As: https://github.com/gitgitgadget/git/releases/tag/pr-756%2Fnipunn1313%2Fdiff_fsmon-v1 Fetch-It-Via: git fetch https://github.com/gitgitgadget/git pr-756/nipunn1313/diff_fsmon-v1 Pull-Request: https://github.com/gitgitgadget/git/pull/756 -- gitgitgadget
