Am 23.06.20 um 19:47 schrieb SZEDER Gábor via GitGitGadget:
> From: =?UTF-8?q?SZEDER=20G=C3=A1bor?= <szeder.dev@xxxxxxxxx>
>
> The file 'dir/subdir/file' can only be modified if its leading
> directories 'dir' and 'dir/subdir' are modified as well.
>
> So when checking modified path Bloom filters looking for commits
> modifying a path with multiple path components, then check not only
> the full path in the Bloom filters, but all its leading directories as
> well. Take care to check these paths in "deepest first" order,
> because it's the full path that is least likely to be modified, and
> the Bloom filter queries can short circuit sooner.
>
> This can significantly reduce the average false positive rate, by
> about an order of magnitude or three(!), and can further speed up
> pathspec-limited revision walks. The table below compares the average
> false positive rate and runtime of
>
> git rev-list HEAD -- "$path"
>
> before and after this change for 5000+ randomly* selected paths from
> each repository:
>
> Average false Average Average
> positive rate runtime runtime
> before after before after difference
> ------------------------------------------------------------------
> git 3.220% 0.7853% 0.0558s 0.0387s -30.6%
> linux 2.453% 0.0296% 0.1046s 0.0766s -26.8%
> tensorflow 2.536% 0.6977% 0.0594s 0.0420s -29.2%
>
> *Path selection was done with the following pipeline:
>
> git ls-tree -r --name-only HEAD | sort -R | head -n 5000
>
> The improvements in runtime are much smaller than the improvements in
> average false positive rate, as we are clearly reaching diminishing
> returns here. However, all these timings depend on that accessing
> tree objects is reasonably fast (warm caches). If we had a partial
> clone and the tree objects had to be fetched from a promisor remote,
> e.g.:
>
> $ git clone --filter=tree:0 --bare file://.../webkit.git webkit.notrees.git
> $ git -C webkit.git -c core.modifiedPathBloomFilters=1 \
> commit-graph write --reachable
> $ cp webkit.git/objects/info/commit-graph webkit.notrees.git/objects/info/
> $ git -C webkit.notrees.git -c core.modifiedPathBloomFilters=1 \
> rev-list HEAD -- "$path"
>
> then checking all leading path component can reduce the runtime from
> over an hour to a few seconds (and this is with the clone and the
> promisor on the same machine).
>
> This adjusts the tracing values in t4216-log-bloom.sh, which provides a
> concrete way to notice the improvement.
>
> Helped-by: Taylor Blau <me@xxxxxxxxxxxx>
> Helped-by: René Scharfe <l.s.r@xxxxxx>
> Signed-off-by: SZEDER Gábor <szeder.dev@xxxxxxxxx>
> Signed-off-by: Derrick Stolee <dstolee@xxxxxxxxxxxxx>
> ---
> revision.c | 41 ++++++++++++++++++++++++++++++++---------
> revision.h | 6 ++++--
> t/t4216-log-bloom.sh | 2 +-
> 3 files changed, 37 insertions(+), 12 deletions(-)
>
> diff --git a/revision.c b/revision.c
> index b53377cd52..077888ee51 100644
> --- a/revision.c
> +++ b/revision.c
> @@ -670,9 +670,10 @@ static void prepare_to_use_bloom_filter(struct rev_info *revs)
> {
> struct pathspec_item *pi;
> char *path_alloc = NULL;
> - const char *path;
> + const char *path, *p;
> int last_index;
> - int len;
> + size_t len;
> + int path_component_nr = 1;
>
> if (!revs->commits)
> return;
> @@ -709,8 +710,28 @@ static void prepare_to_use_bloom_filter(struct rev_info *revs)
> return;
> }
>
> - revs->bloom_key = xmalloc(sizeof(struct bloom_key));
> - fill_bloom_key(path, len, revs->bloom_key, revs->bloom_filter_settings);
> + p = path;
> + while (*p) {
> + if (is_dir_sep(*p))
> + path_component_nr++;
> + p++;
> + }
> +
> + revs->bloom_keys_nr = path_component_nr;
> + ALLOC_ARRAY(revs->bloom_keys, revs->bloom_keys_nr);
> +
> + fill_bloom_key(path, len, &revs->bloom_keys[0],
> + revs->bloom_filter_settings);
> + path_component_nr = 1;
> +
> + p = path + len - 1;
len cannot be 0 at this point, as patch 9 made sure, so this is safe.
Good.
> + while (p > path) {
> + if (is_dir_sep(*p))
> + fill_bloom_key(path, p - path,
> + &revs->bloom_keys[path_component_nr++],
> + revs->bloom_filter_settings);
> + p--;
> + }
This walks the directory hierarchy upwards and adds bloom filters for
shorter and shorter paths, ("deepest first"). Good.
And it supports all directory separators. On Windows that would be
slash (/) and backslash (\). I assume paths are normalized to use
only slashes when bloom filters are written, correct? Then the lookup
side needs to normalize a given path to only use slashes as well,
otherwise paths with backslashes cannot be found. This part seems to
be missing.
>
> if (trace2_is_enabled() && !bloom_filter_atexit_registered) {
> atexit(trace2_bloom_filter_statistics_atexit);
> @@ -724,7 +745,7 @@ static int check_maybe_different_in_bloom_filter(struct rev_info *revs,
> struct commit *commit)
> {
> struct bloom_filter *filter;
> - int result;
> + int result = 1, j;
>
> if (!revs->repo->objects->commit_graph)
> return -1;
> @@ -744,9 +765,11 @@ static int check_maybe_different_in_bloom_filter(struct rev_info *revs,
> return -1;
> }
>
> - result = bloom_filter_contains(filter,
> - revs->bloom_key,
> - revs->bloom_filter_settings);
> + for (j = 0; result && j < revs->bloom_keys_nr; j++) {
> + result = bloom_filter_contains(filter,
> + &revs->bloom_keys[j],
> + revs->bloom_filter_settings);
> + }
>
> if (result)
> count_bloom_filter_maybe++;
> @@ -786,7 +809,7 @@ static int rev_compare_tree(struct rev_info *revs,
> return REV_TREE_SAME;
> }
>
> - if (revs->bloom_key && !nth_parent) {
> + if (revs->bloom_keys_nr && !nth_parent) {
> bloom_ret = check_maybe_different_in_bloom_filter(revs, commit);
>
> if (bloom_ret == 0)
> diff --git a/revision.h b/revision.h
> index 7c026fe41f..abbfb4ab59 100644
> --- a/revision.h
> +++ b/revision.h
> @@ -295,8 +295,10 @@ struct rev_info {
> struct topo_walk_info *topo_walk_info;
>
> /* Commit graph bloom filter fields */
> - /* The bloom filter key for the pathspec */
> - struct bloom_key *bloom_key;
> + /* The bloom filter key(s) for the pathspec */
> + struct bloom_key *bloom_keys;
> + int bloom_keys_nr;
> +
> /*
> * The bloom filter settings used to generate the key.
> * This is loaded from the commit-graph being used.
> diff --git a/t/t4216-log-bloom.sh b/t/t4216-log-bloom.sh
> index f890cc4737..84f95972ca 100755
> --- a/t/t4216-log-bloom.sh
> +++ b/t/t4216-log-bloom.sh
> @@ -146,7 +146,7 @@ test_expect_success 'setup - add commit-graph to the chain with Bloom filters' '
>
> test_bloom_filters_used_when_some_filters_are_missing () {
> log_args=$1
> - bloom_trace_prefix="statistics:{\"filter_not_present\":3,\"zero_length_filter\":0,\"maybe\":8,\"definitely_not\":6"
> + bloom_trace_prefix="statistics:{\"filter_not_present\":3,\"zero_length_filter\":0,\"maybe\":6,\"definitely_not\":8"
> setup "$log_args" &&
> grep -q "$bloom_trace_prefix" "$TRASH_DIRECTORY/trace.perf" &&
> test_cmp log_wo_bloom log_w_bloom
>
