| Message ID | b75b534446088b20e77cbaa7f09705510ddec908.1617991824.git.me@ttaylorr.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | multi-pack reachability bitmaps | expand |
> There is slight overhead in "simulated clone", "simulated partial > clone", and "clone (partial bitmap)". Unsurprisingly, that overhead is > due to using the MIDX's reverse index to map between bit positions and > MIDX positions. Thanks - it's great to see that accessing a MIDX bitmap doesn't add much overhead (as compared to accessing a single-pack bitmap of the same size). All the remaining patches up to and including this one look good. Overall, I did have some comments here and there, but I am happy with the overall design.
Jonathan Tan <jonathantanmy@google.com> writes: >> There is slight overhead in "simulated clone", "simulated partial >> clone", and "clone (partial bitmap)". Unsurprisingly, that overhead is >> due to using the MIDX's reverse index to map between bit positions and >> MIDX positions. > > Thanks - it's great to see that accessing a MIDX bitmap doesn't add much > overhead (as compared to accessing a single-pack bitmap of the same > size). > > All the remaining patches up to and including this one look good. > Overall, I did have some comments here and there, but I am happy with > the overall design. Thanks for a review.
diff --git a/t/perf/p5326-multi-pack-bitmaps.sh b/t/perf/p5326-multi-pack-bitmaps.sh new file mode 100755 index 0000000000..5845109ac7 --- /dev/null +++ b/t/perf/p5326-multi-pack-bitmaps.sh @@ -0,0 +1,43 @@ +#!/bin/sh + +test_description='Tests performance using midx bitmaps' +. ./perf-lib.sh +. "${TEST_DIRECTORY}/perf/lib-bitmap.sh" + +test_perf_large_repo + +test_expect_success 'enable multi-pack index' ' + git config core.multiPackIndex true +' + +test_perf 'setup multi-pack index' ' + git repack -ad && + git multi-pack-index write --bitmap +' + +test_full_bitmap + +test_expect_success 'create partial bitmap state' ' + # pick a commit to represent the repo tip in the past + cutoff=$(git rev-list HEAD~100 -1) && + orig_tip=$(git rev-parse HEAD) && + + # now pretend we have just one tip + rm -rf .git/logs .git/refs/* .git/packed-refs && + git update-ref HEAD $cutoff && + + # and then repack, which will leave us with a nice + # big bitmap pack of the "old" history, and all of + # the new history will be loose, as if it had been pushed + # up incrementally and exploded via unpack-objects + git repack -Ad && + git multi-pack-index write --bitmap && + + # and now restore our original tip, as if the pushes + # had happened + git update-ref HEAD $orig_tip +' + +test_partial_bitmap + +test_done
These new performance tests demonstrate effectively the same behavior as p5310, but use a multi-pack bitmap instead of a single-pack one. Notably, p5326 does not create a MIDX bitmap with multiple packs. This is so we can measure a direct comparison between it and p5310. Any difference between the two is measuring just the overhead of using MIDX bitmaps. Here are the results of p5310 and p5326 together, measured at the same time and on the same machine (using a Xenon W-2255 CPU): Test HEAD ------------------------------------------------------------------------ 5310.2: repack to disk 96.78(93.39+11.33) 5310.3: simulated clone 9.98(9.79+0.19) 5310.4: simulated fetch 1.75(4.26+0.19) 5310.5: pack to file (bitmap) 28.20(27.87+8.70) 5310.6: rev-list (commits) 0.41(0.36+0.05) 5310.7: rev-list (objects) 1.61(1.54+0.07) 5310.8: rev-list count with blob:none 0.25(0.21+0.04) 5310.9: rev-list count with blob:limit=1k 2.65(2.54+0.10) 5310.10: rev-list count with tree:0 0.23(0.19+0.04) 5310.11: simulated partial clone 4.34(4.21+0.12) 5310.13: clone (partial bitmap) 11.05(12.21+0.48) 5310.14: pack to file (partial bitmap) 31.25(34.22+3.70) 5310.15: rev-list with tree filter (partial bitmap) 0.26(0.22+0.04) versus the same tests (this time using a multi-pack index): Test HEAD ------------------------------------------------------------------------ 5326.2: setup multi-pack index 78.99(75.29+11.58) 5326.3: simulated clone 11.78(11.56+0.22) 5326.4: simulated fetch 1.70(4.49+0.13) 5326.5: pack to file (bitmap) 28.02(27.72+8.76) 5326.6: rev-list (commits) 0.42(0.36+0.06) 5326.7: rev-list (objects) 1.65(1.58+0.06) 5326.8: rev-list count with blob:none 0.26(0.21+0.05) 5326.9: rev-list count with blob:limit=1k 2.97(2.86+0.10) 5326.10: rev-list count with tree:0 0.25(0.20+0.04) 5326.11: simulated partial clone 5.65(5.49+0.16) 5326.13: clone (partial bitmap) 12.22(13.43+0.38) 5326.14: pack to file (partial bitmap) 30.05(31.57+7.25) 5326.15: rev-list with tree filter (partial bitmap) 0.24(0.20+0.04) There is slight overhead in "simulated clone", "simulated partial clone", and "clone (partial bitmap)". Unsurprisingly, that overhead is due to using the MIDX's reverse index to map between bit positions and MIDX positions. This can be reproduced by running "git repack -adb" along with "git multi-pack-index write --bitmap" in a large-ish repository. Then run: $ perf record -o pack.perf git -c core.multiPackIndex=false \ pack-objects --all --stdout >/dev/null </dev/null $ perf record -o midx.perf git -c core.multiPackIndex=true \ pack-objects --all --stdout >/dev/null </dev/null and compare the two with "perf diff -c delta -o 1 pack.perf midx.perf". The most notable results are below (the next largest positive delta is +0.14%): # Event 'cycles' # # Baseline Delta Shared Object Symbol # ........ ....... .................. .......................... # +5.86% git [.] nth_midxed_offset +5.24% git [.] nth_midxed_pack_int_id 3.45% +0.97% git [.] offset_to_pack_pos 3.30% +0.57% git [.] pack_pos_to_offset +0.30% git [.] pack_pos_to_midx Signed-off-by: Taylor Blau <me@ttaylorr.com> --- t/perf/p5326-multi-pack-bitmaps.sh | 43 ++++++++++++++++++++++++++++++ 1 file changed, 43 insertions(+) create mode 100755 t/perf/p5326-multi-pack-bitmaps.sh