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* [PATCH 0/3] pack-bitmap: boundary-based bitmap traversal
@ 2023-04-25  0:00 Taylor Blau
  2023-04-25  0:00 ` [PATCH 1/3] revision: support tracking uninteresting commits Taylor Blau
                   ` (8 more replies)
  0 siblings, 9 replies; 51+ messages in thread
From: Taylor Blau @ 2023-04-25  0:00 UTC (permalink / raw)
  To: git; +Cc: Jeff King, Derrick Stolee, Junio C Hamano

Here is a short (but dense) series that I worked on towards the end of
2021 with Peff.

Its goal is to improve the bitmap traversal we implement in
prepare_bitmap_walk(). Specifically, it avoids building up a complete
bitmap of the "haves" side, and instead uses a combination of (a)
UNINTERESTING commits between the tips and boundary, and (b) the
boundary itself.

The gory details are laid out in 3/3, but the high-level overview of the
new algorithm to compute the set of objects between "haves" and "wants"
using bitmaps is:

  1. Build a (partial) bitmap of the haves side by first OR-ing any
     bitmap(s) that already exist for UNINTERESTING commits between the
     haves and the boundary.

  2. For each commit along the boundary, add it as a fill-in traversal
     tip (where the traversal terminates once an existing bitmap is
     found), and perform fill-in traversal.

  3. Build up a complete bitmap of the wants side as usual, stopping any
     time we intersect the (partial) haves side.

This improves many cases where using bitmaps was significantly *slower*
than regular, non-bitmap traversal. In some instances, using bitmaps is
still slower than the non-bitmap case, but it is a substantial
improvement over the classic bitmap walk.

    $ ours="$(git branch --show-current)"
      argv="--count --objects $ours --not --exclude=$ours --branches"
      hyperfine \
        -n 'no bitmaps' "git.compile rev-list $argv" \
        -n 'existing bitmap traversal' "git rev-list --use-bitmap-index $argv" \
        -n 'this commit' "git.compile rev-list --use-bitmap-index $argv"
    Benchmark 1: no bitmaps
      Time (mean ± σ):      15.1 ms ±   4.1 ms    [User: 8.1 ms, System: 6.9 ms]
      Range (min … max):     7.4 ms …  21.8 ms    131 runs

    Benchmark 2: existing bitmap traversal
      Time (mean ± σ):      82.6 ms ±   9.2 ms    [User: 63.6 ms, System: 19.0 ms]
      Range (min … max):    73.8 ms … 105.4 ms    28 runs

    Benchmark 3: this commit
      Time (mean ± σ):      19.8 ms ±   3.1 ms    [User: 13.0 ms, System: 6.8 ms]
      Range (min … max):    17.7 ms …  38.6 ms    158 runs

    Summary
      'no bitmaps' ran
        1.31 ± 0.41 times faster than 'this commit'
        5.49 ± 1.62 times faster than 'existing bitmap traversal'

In a large repository on GitHub.com, the timings to compute the objects
unique to "master", as in:

    $ git rev-list --count --objects master --not --exclude=master --branches

improve as follows:

  - 1.012 sec (without bitmaps)
  - 29.571 sec (with the existing bitmap walk)
  - 2.279 sec (with these patches)

The first couple of patches are preparatory, and the third patch is the
substantive one.

Please have a look and poke any holes you can find in the new approach
:-). Thanks in advance for your review.

Taylor Blau (3):
  revision: support tracking uninteresting commits
  pack-bitmap.c: extract `fill_in_bitmap()`
  pack-bitmap.c: use commit boundary during bitmap traversal

 pack-bitmap.c | 252 ++++++++++++++++++++++++++++++++++++++------------
 revision.c    |  10 +-
 revision.h    |   5 +
 3 files changed, 205 insertions(+), 62 deletions(-)

-- 
2.40.0.380.gda896aa358.dirty

^ permalink raw reply	[flat|nested] 51+ messages in thread

end of thread, other threads:[~2023-06-08 16:25 UTC | newest]

Thread overview: 51+ messages (download: mbox.gz / follow: Atom feed)
-- links below jump to the message on this page --
2023-04-25  0:00 [PATCH 0/3] pack-bitmap: boundary-based bitmap traversal Taylor Blau
2023-04-25  0:00 ` [PATCH 1/3] revision: support tracking uninteresting commits Taylor Blau
2023-04-25 18:15   ` Derrick Stolee
2023-05-03 21:48     ` Taylor Blau
2023-05-04 13:46       ` Derrick Stolee
2023-05-03 22:08     ` Taylor Blau
2023-05-04 13:59       ` Derrick Stolee
2023-05-05 17:30         ` Taylor Blau
2023-04-25 18:22   ` Junio C Hamano
2023-04-25 18:48     ` Taylor Blau
2023-04-25  0:00 ` [PATCH 2/3] pack-bitmap.c: extract `fill_in_bitmap()` Taylor Blau
2023-04-25 18:32   ` Junio C Hamano
2023-04-25 18:51     ` [PATCH 2/3] pack-bitmap.c: extract `fill_in_bitmap()`t Taylor Blau
2023-04-25  0:00 ` [PATCH 3/3] pack-bitmap.c: use commit boundary during bitmap traversal Taylor Blau
2023-04-25 18:52   ` Junio C Hamano
2023-05-02 21:31     ` Felipe Contreras
2023-05-03 21:42     ` Taylor Blau
2023-05-03 21:58       ` Junio C Hamano
2023-04-25 18:53   ` Derrick Stolee
2023-04-25 18:02 ` [PATCH 0/3] pack-bitmap: boundary-based " Junio C Hamano
2023-04-25 18:30   ` Derrick Stolee
2023-04-25 18:57     ` Taylor Blau
2023-04-25 19:52       ` Derrick Stolee
2023-05-03 21:43         ` Taylor Blau
2023-04-25 18:06 ` Derrick Stolee
2023-04-25 19:01   ` Taylor Blau
2023-04-25 20:27     ` Derrick Stolee
2023-05-01 22:08 ` Junio C Hamano
2023-05-02 23:52   ` Taylor Blau
2023-05-05 17:27 ` [PATCH v2 0/2] " Taylor Blau
2023-05-05 17:27   ` [PATCH v2 1/2] pack-bitmap.c: extract `fill_in_bitmap()` Taylor Blau
2023-05-05 17:27   ` [PATCH v2 2/2] pack-bitmap.c: use commit boundary during bitmap traversal Taylor Blau
2023-05-05 18:13     ` Derrick Stolee
2023-05-05 18:43       ` Taylor Blau
2023-05-05 17:33   ` [PATCH v2 0/2] pack-bitmap: boundary-based " Junio C Hamano
2023-05-05 17:59   ` Derrick Stolee
2023-05-05 18:46     ` [PATCH v2 0/2] pack-bitmap: boundary-based bitmap traversalt Taylor Blau
2023-05-05 20:45       ` Derrick Stolee
2023-05-08 17:38 ` [PATCH v3 0/3] pack-bitmap: boundary-based bitmap traversal Taylor Blau
2023-05-08 17:38   ` [PATCH v3 1/3] object: add object_array initializer helper function Taylor Blau
2023-05-08 17:38   ` [PATCH v3 2/3] pack-bitmap.c: extract `fill_in_bitmap()` Taylor Blau
2023-05-08 17:38   ` [PATCH v3 3/3] pack-bitmap.c: use commit boundary during bitmap traversal Taylor Blau
2023-05-08 20:53     ` Derrick Stolee
2023-05-08 22:12       ` Taylor Blau
2023-05-10 22:55   ` [PATCH v3 0/3] pack-bitmap: boundary-based " Junio C Hamano
2023-05-10 23:10     ` Taylor Blau
2023-05-11 15:23       ` Derrick Stolee
2023-06-08 16:25 ` [PATCH v4 " Taylor Blau
2023-06-08 16:25   ` [PATCH v4 1/3] object: add object_array initializer helper function Taylor Blau
2023-06-08 16:25   ` [PATCH v4 2/3] pack-bitmap.c: extract `fill_in_bitmap()` Taylor Blau
2023-06-08 16:25   ` [PATCH v4 3/3] pack-bitmap.c: use commit boundary during bitmap traversal Taylor Blau

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