git@vger.kernel.org list mirror (unofficial, one of many)
 help / color / Atom feed
From: Derrick Stolee <stolee@gmail.com>
To: Jeff King <peff@peff.net>
Cc: Garima Singh via GitGitGadget <gitgitgadget@gmail.com>,
	git@vger.kernel.org, szeder.dev@gmail.com,
	jonathantanmy@google.com, jeffhost@microsoft.com,
	me@ttaylorr.com, Junio C Hamano <gitster@pobox.com>
Subject: Re: [PATCH 1/3] commit-graph: examine changed-path objects in pack order
Date: Mon, 30 Dec 2019 09:37:28 -0500
Message-ID: <b9bd0c2e-63fc-5658-7a24-b8ab078acd44@gmail.com> (raw)
In-Reply-To: <20191229061246.GB220034@coredump.intra.peff.net>

On 12/29/2019 1:12 AM, Jeff King wrote:
> On Fri, Dec 27, 2019 at 09:51:02AM -0500, Derrick Stolee wrote:
> 
>> On 12/22/2019 4:32 AM, Jeff King wrote:
>>> Looking at the diff of commit objects in pack order is much faster than
>>> in sha1 order, as it gives locality to the access of tree deltas
>>> (whereas sha1 order is effectively random). Unfortunately the
>>> commit-graph code sorts the commits (several times, sometimes as an oid
>>> and sometimes a pointer-to-commit), and we ultimately traverse in sha1
>>> order.
>>>
>>> Instead, let's remember the position at which we see each commit, and
>>> traverse in that order when looking at bloom filters. This drops my time
>>> for "git commit-graph write --changed-paths" in linux.git from ~4
>>> minutes to ~1.5 minutes.
>>
>> I'm doing my own perf tests on these patches, and my copy of linux.git
>> has four packs of varying sizes (corresponding with my rare fetches and
>> lack of repacks). My time goes from 3m50s to 3m00s. I was confused at
>> first, but then realized that I used the "--reachable" flag. In that
>> case, we never run set_commit_pos(), so all positions are equal and the
>> sort is not helpful.
>>
>> I thought that inserting some set_commit_pos() calls into close_reachable()
>> and add_missing_parents() would give some amount of time-order to the
>> commits as we compute the filters. However, the time did not change at
>> all.
>>
>> I've included the patch below for reference, anyway.
> 
> Yeah, I expected that would cover it, too. But instrumenting it to dump
> the position of each commit (see patch below), and then decorating "git
> log" output with the positions (see script below) shows that we're all
> over the map:
> 
>   *   3
>   |\  
>   | * 2791
>   | * 5476
>   | * 8520
>   | * 12040
>   | * 16036
>   * |   2790
>   |\ \  
>   | * | 5475
>   | * | 8519
>   | * | 12039
>   | * | 16035
>   | * | 20517
>   | * | 25527
>   | |/  
>   * |   5474
>   |\ \  
>   | * | 8518
>   | * | 12038
>   * | |   8517
>   [...]

This makes a lot of sense why the previous approach did not work. Thanks!

> I think the root issue is that we never do any date-sorting on the
> commits. So:
> 
>   - we hit each ref tip in lexical order; with tags, this is quite often
>     the opposite of reverse-chronological
> 
>   - we traverse breadth-first, but we don't order queue at all. So if we
>     see a merge X, then we'll next process X^1 and X^2, and then X^1^,
>     and then X^2^, and so forth. So we keep digging equally down
>     simultaneous branches, even if one branch is way shorter than the
>     other. Whereas a regular Git traversal will order the queue by
>     commit timestamp, so it tends to be roughly chronological (of course
>     a topo-sort would work too, but that's probably overkill).
> 
> I wonder if this would be simpler if "commit-graph --reachable" just
> used the regular revision machinery instead of doing its own custom
> traversal.

Instead, why not use our already-computed generation numbers? That seems
to improve the time a bit. (6m30s to 4m50s)

-->8--

From: Derrick Stolee <dstolee@microsoft.com>
Date: Fri, 27 Dec 2019 09:47:49 -0500
Subject: [PATCH] commit-graph: examine commits by generation number

When running 'git commit-graph write --changed-paths', we sort the
commits by pack-order to save time when computing the changed-paths
bloom filters. This does not help when finding the commits via the
--reachable flag.

If not using pack-order, then sort by generation number before
examining the diff. Commits with similar generation are more likely
to have many trees in common, making the diff faster.

On the Linux kernel repository, this change reduced the computation
time for 'git commit-graph write --reachable --changed-paths' from
6m30s to 4m50s.

Helped-by: Jeff King <peff@peff.net>
Signed-off-by: Derrick Stolee <dstolee@microsoft.com>
---
 commit-graph.c | 33 ++++++++++++++++++++++++++++++---
 1 file changed, 30 insertions(+), 3 deletions(-)

diff --git a/commit-graph.c b/commit-graph.c
index bf6c663772..fe4ab545f2 100644
--- a/commit-graph.c
+++ b/commit-graph.c
@@ -72,6 +72,25 @@ static int commit_pos_cmp(const void *va, const void *vb)
 	       commit_pos_at(&commit_pos, b);
 }
 
+static int commit_gen_cmp(const void *va, const void *vb)
+{
+	const struct commit *a = *(const struct commit **)va;
+	const struct commit *b = *(const struct commit **)vb;
+
+	/* lower generation commits first */
+	if (a->generation < b->generation)
+		return -1;
+	else if (a->generation > b->generation)
+		return 1;
+
+	/* use date as a heuristic when generations are equal */
+	if (a->date < b->date)
+		return -1;
+	else if (a->date > b->date)
+		return 1;
+	return 0;
+}
+
 char *get_commit_graph_filename(const char *obj_dir)
 {
 	char *filename = xstrfmt("%s/info/commit-graph", obj_dir);
@@ -849,7 +868,8 @@ struct write_commit_graph_context {
 		 report_progress:1,
 		 split:1,
 		 check_oids:1,
-		 bloom:1;
+		 bloom:1,
+		 order_by_pack:1;
 
 	const struct split_commit_graph_opts *split_opts;
 	uint32_t total_bloom_filter_size;
@@ -1245,7 +1265,11 @@ static void compute_bloom_filters(struct write_commit_graph_context *ctx)
 
 	ALLOC_ARRAY(sorted_by_pos, ctx->commits.nr);
 	COPY_ARRAY(sorted_by_pos, ctx->commits.list, ctx->commits.nr);
-	QSORT(sorted_by_pos, ctx->commits.nr, commit_pos_cmp);
+
+	if (ctx->order_by_pack)
+		QSORT(sorted_by_pos, ctx->commits.nr, commit_pos_cmp);
+	else
+		QSORT(sorted_by_pos, ctx->commits.nr, commit_gen_cmp);
 
 	for (i = 0; i < ctx->commits.nr; i++) {
 		struct commit *c = sorted_by_pos[i];
@@ -1979,6 +2003,7 @@ int write_commit_graph(const char *obj_dir,
 	}
 
 	if (pack_indexes) {
+		ctx->order_by_pack = 1;
 		if ((res = fill_oids_from_packs(ctx, pack_indexes)))
 			goto cleanup;
 	}
@@ -1988,8 +2013,10 @@ int write_commit_graph(const char *obj_dir,
 			goto cleanup;
 	}
 
-	if (!pack_indexes && !commit_hex)
+	if (!pack_indexes && !commit_hex) {
+		ctx->order_by_pack = 1;
 		fill_oids_from_all_packs(ctx);
+	}
 
 	close_reachable(ctx);
 
-- 
2.25.0.rc0




  parent reply index

Thread overview: 141+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-12-20 22:05 [PATCH 0/9] [RFC] Changed Paths Bloom Filters Garima Singh via GitGitGadget
2019-12-20 22:05 ` [PATCH 1/9] commit-graph: add --changed-paths option to write Garima Singh via GitGitGadget
2020-01-01 20:20   ` Jakub Narebski
2019-12-20 22:05 ` [PATCH 2/9] commit-graph: write changed paths bloom filters Garima Singh via GitGitGadget
2019-12-21 16:48   ` Philip Oakley
2020-01-06 18:44   ` Jakub Narebski
2020-01-13 19:48     ` Garima Singh
2019-12-20 22:05 ` [PATCH 3/9] commit-graph: use MAX_NUM_CHUNKS Garima Singh via GitGitGadget
2020-01-07 12:19   ` Jakub Narebski
2019-12-20 22:05 ` [PATCH 4/9] commit-graph: document bloom filter format Garima Singh via GitGitGadget
2020-01-07 14:46   ` Jakub Narebski
2019-12-20 22:05 ` [PATCH 5/9] commit-graph: write changed path bloom filters to commit-graph file Garima Singh via GitGitGadget
2020-01-07 16:01   ` Jakub Narebski
2020-01-14 15:14     ` Garima Singh
2019-12-20 22:05 ` [PATCH 6/9] commit-graph: test commit-graph write --changed-paths Garima Singh via GitGitGadget
2020-01-08  0:32   ` Jakub Narebski
2019-12-20 22:05 ` [PATCH 7/9] commit-graph: reuse existing bloom filters during write Garima Singh via GitGitGadget
2020-01-09 19:12   ` Jakub Narebski
2019-12-20 22:05 ` [PATCH 8/9] revision.c: use bloom filters to speed up path based revision walks Garima Singh via GitGitGadget
2020-01-11  0:27   ` Jakub Narebski
2020-01-15  0:08     ` Garima Singh
2019-12-20 22:05 ` [PATCH 9/9] commit-graph: add GIT_TEST_COMMIT_GRAPH_BLOOM_FILTERS test flag Garima Singh via GitGitGadget
2020-01-11 19:56   ` Jakub Narebski
2020-01-15  0:55     ` Garima Singh
2019-12-20 22:14 ` [PATCH 0/9] [RFC] Changed Paths Bloom Filters Junio C Hamano
2019-12-22  9:26 ` Christian Couder
2019-12-22  9:38   ` Jeff King
2020-01-01 12:04     ` Jakub Narebski
2019-12-22  9:30 ` Jeff King
2019-12-22  9:32   ` [PATCH 1/3] commit-graph: examine changed-path objects in pack order Jeff King
2019-12-27 14:51     ` Derrick Stolee
2019-12-29  6:12       ` Jeff King
2019-12-29  6:28         ` Jeff King
2019-12-30 14:37         ` Derrick Stolee [this message]
2019-12-30 14:51           ` Derrick Stolee
2019-12-22  9:32   ` [PATCH 2/3] commit-graph: free large diffs, too Jeff King
2019-12-27 14:52     ` Derrick Stolee
2019-12-22  9:32   ` [PATCH 3/3] commit-graph: stop using full rev_info for diffs Jeff King
2019-12-27 14:53     ` Derrick Stolee
2019-12-26 14:21   ` [PATCH 0/9] [RFC] Changed Paths Bloom Filters Derrick Stolee
2019-12-29  6:03     ` Jeff King
2019-12-27 16:11   ` Derrick Stolee
2019-12-29  6:24     ` Jeff King
2019-12-30 16:04       ` Derrick Stolee
2019-12-30 17:02       ` Junio C Hamano
2019-12-31 16:45 ` Jakub Narebski
2020-01-13 16:54   ` Garima Singh
2020-01-20 13:48     ` Jakub Narebski
2020-01-21 16:14       ` Garima Singh
2020-02-02 18:43         ` Jakub Narebski
2020-01-21 23:40 ` Emily Shaffer
2020-01-27 18:24   ` Garima Singh
2020-02-01 23:32   ` Jakub Narebski
2020-02-05 22:56 ` [PATCH v2 00/11] " Garima Singh via GitGitGadget
2020-02-05 22:56   ` [PATCH v2 01/11] commit-graph: use MAX_NUM_CHUNKS Garima Singh via GitGitGadget
2020-02-09 12:39     ` Jakub Narebski
2020-02-05 22:56   ` [PATCH v2 02/11] bloom: core Bloom filter implementation for changed paths Garima Singh via GitGitGadget
2020-02-15 17:17     ` Jakub Narebski
2020-02-16 16:49     ` Jakub Narebski
2020-02-22  0:32       ` Garima Singh
2020-02-23 13:38         ` Jakub Narebski
2020-02-24 17:34           ` Garima Singh
2020-02-24 18:20             ` Jakub Narebski
2020-02-05 22:56   ` [PATCH v2 03/11] diff: halt tree-diff early after max_changes Derrick Stolee via GitGitGadget
2020-02-17  0:00     ` Jakub Narebski
2020-02-22  0:37       ` Garima Singh
2020-02-05 22:56   ` [PATCH v2 04/11] commit-graph: compute Bloom filters for changed paths Garima Singh via GitGitGadget
2020-02-17 21:56     ` Jakub Narebski
2020-02-22  0:55       ` Garima Singh
2020-02-23 17:34         ` Jakub Narebski
2020-02-05 22:56   ` [PATCH v2 05/11] commit-graph: examine changed-path objects in pack order Jeff King via GitGitGadget
2020-02-18 17:59     ` Jakub Narebski
2020-02-24 18:29       ` Garima Singh
2020-02-05 22:56   ` [PATCH v2 06/11] commit-graph: examine commits by generation number Derrick Stolee via GitGitGadget
2020-02-19  0:32     ` Jakub Narebski
2020-02-24 20:45       ` Garima Singh
2020-02-05 22:56   ` [PATCH v2 07/11] commit-graph: write Bloom filters to commit graph file Garima Singh via GitGitGadget
2020-02-19 15:13     ` Jakub Narebski
2020-02-24 21:14       ` Garima Singh
2020-02-25 11:40         ` Jakub Narebski
2020-02-25 15:58           ` Garima Singh
2020-02-05 22:56   ` [PATCH v2 08/11] commit-graph: reuse existing Bloom filters during write Garima Singh via GitGitGadget
2020-02-20 18:48     ` Jakub Narebski
2020-02-24 21:45       ` Garima Singh
2020-02-05 22:56   ` [PATCH v2 09/11] commit-graph: add --changed-paths option to write subcommand Garima Singh via GitGitGadget
2020-02-20 20:28     ` Jakub Narebski
2020-02-24 21:51       ` Garima Singh
2020-02-25 12:10         ` Jakub Narebski
2020-02-20 22:10     ` Bryan Turner
2020-02-22  1:44       ` Garima Singh
2020-02-05 22:56   ` [PATCH v2 10/11] revision.c: use Bloom filters to speed up path based revision walks Garima Singh via GitGitGadget
2020-02-21 17:31     ` Jakub Narebski
2020-02-21 22:45     ` Jakub Narebski
2020-02-05 22:56   ` [PATCH v2 11/11] commit-graph: add GIT_TEST_COMMIT_GRAPH_CHANGED_PATHS test flag Garima Singh via GitGitGadget
2020-02-22  0:11     ` Jakub Narebski
2020-02-07 13:52   ` [PATCH v2 00/11] Changed Paths Bloom Filters SZEDER Gábor
2020-02-07 15:09     ` Garima Singh
2020-02-07 15:36       ` Derrick Stolee
2020-02-07 16:15         ` SZEDER Gábor
2020-02-07 16:33           ` Derrick Stolee
2020-02-11 19:08       ` Garima Singh
2020-02-08 23:04   ` Jakub Narebski
2020-02-21 17:41     ` Garima Singh
2020-03-29 18:36       ` Junio C Hamano
2020-03-30  0:31   ` [PATCH v3 00/16] " Garima Singh via GitGitGadget
2020-03-30  0:31     ` [PATCH v3 01/16] commit-graph: define and use MAX_NUM_CHUNKS Garima Singh via GitGitGadget
2020-03-30  0:31     ` [PATCH v3 02/16] bloom.c: add the murmur3 hash implementation Garima Singh via GitGitGadget
2020-03-30  0:31     ` [PATCH v3 03/16] bloom.c: introduce core Bloom filter constructs Garima Singh via GitGitGadget
2020-03-30  0:31     ` [PATCH v3 04/16] bloom.c: core Bloom filter implementation for changed paths Garima Singh via GitGitGadget
2020-03-30  0:31     ` [PATCH v3 05/16] diff: halt tree-diff early after max_changes Derrick Stolee via GitGitGadget
2020-03-30  0:31     ` [PATCH v3 06/16] commit-graph: compute Bloom filters for changed paths Garima Singh via GitGitGadget
2020-03-30  0:31     ` [PATCH v3 07/16] commit-graph: examine changed-path objects in pack order Jeff King via GitGitGadget
2020-03-30  0:31     ` [PATCH v3 08/16] commit-graph: examine commits by generation number Garima Singh via GitGitGadget
2020-03-30  0:31     ` [PATCH v3 09/16] diff: skip batch object download when possible Garima Singh via GitGitGadget
2020-03-30  0:31     ` [PATCH v3 10/16] commit-graph: write Bloom filters to commit graph file Garima Singh via GitGitGadget
2020-03-30  0:31     ` [PATCH v3 11/16] commit-graph: reuse existing Bloom filters during write Garima Singh via GitGitGadget
2020-03-30  0:31     ` [PATCH v3 12/16] commit-graph: add --changed-paths option to write subcommand Garima Singh via GitGitGadget
2020-03-30  0:31     ` [PATCH v3 13/16] revision.c: use Bloom filters to speed up path based revision walks Garima Singh via GitGitGadget
2020-03-30  0:31     ` [PATCH v3 14/16] revision.c: add trace2 stats around Bloom filter usage Garima Singh via GitGitGadget
2020-03-30  0:31     ` [PATCH v3 15/16] t4216: add end to end tests for git log with Bloom filters Garima Singh via GitGitGadget
2020-03-30  0:31     ` [PATCH v3 16/16] commit-graph: add GIT_TEST_COMMIT_GRAPH_CHANGED_PATHS test flag Garima Singh via GitGitGadget
2020-04-06 16:59     ` [PATCH v4 00/15] Changed Paths Bloom Filters Garima Singh via GitGitGadget
2020-04-06 16:59       ` [PATCH v4 01/15] commit-graph: define and use MAX_NUM_CHUNKS Garima Singh via GitGitGadget
2020-04-06 16:59       ` [PATCH v4 02/15] bloom.c: add the murmur3 hash implementation Garima Singh via GitGitGadget
2020-04-06 16:59       ` [PATCH v4 03/15] bloom.c: introduce core Bloom filter constructs Garima Singh via GitGitGadget
2020-04-06 16:59       ` [PATCH v4 04/15] bloom.c: core Bloom filter implementation for changed paths Garima Singh via GitGitGadget
2020-04-06 16:59       ` [PATCH v4 05/15] diff: halt tree-diff early after max_changes Derrick Stolee via GitGitGadget
2020-04-06 16:59       ` [PATCH v4 06/15] commit-graph: compute Bloom filters for changed paths Garima Singh via GitGitGadget
2020-04-06 16:59       ` [PATCH v4 07/15] commit-graph: examine changed-path objects in pack order Jeff King via GitGitGadget
2020-04-06 16:59       ` [PATCH v4 08/15] commit-graph: examine commits by generation number Garima Singh via GitGitGadget
2020-04-06 16:59       ` [PATCH v4 09/15] commit-graph: write Bloom filters to commit graph file Garima Singh via GitGitGadget
2020-04-06 16:59       ` [PATCH v4 10/15] commit-graph: reuse existing Bloom filters during write Garima Singh via GitGitGadget
2020-04-06 16:59       ` [PATCH v4 11/15] commit-graph: add --changed-paths option to write subcommand Garima Singh via GitGitGadget
2020-04-06 16:59       ` [PATCH v4 12/15] revision.c: use Bloom filters to speed up path based revision walks Garima Singh via GitGitGadget
2020-04-06 16:59       ` [PATCH v4 13/15] revision.c: add trace2 stats around Bloom filter usage Garima Singh via GitGitGadget
2020-04-06 16:59       ` [PATCH v4 14/15] t4216: add end to end tests for git log with Bloom filters Garima Singh via GitGitGadget
2020-04-06 16:59       ` [PATCH v4 15/15] commit-graph: add GIT_TEST_COMMIT_GRAPH_CHANGED_PATHS test flag Garima Singh via GitGitGadget
2020-04-08 15:51       ` [PATCH v4 00/15] Changed Paths Bloom Filters Derrick Stolee
2020-04-08 19:21         ` Junio C Hamano
2020-04-08 20:05         ` Jakub Narębski
2020-03-05 19:49 ` [PATCH 0/9] [RFC] " Garima Singh

Reply instructions:

You may reply publicly to this message via plain-text email
using any one of the following methods:

* Save the following mbox file, import it into your mail client,
  and reply-to-all from there: mbox

  Avoid top-posting and favor interleaved quoting:
  https://en.wikipedia.org/wiki/Posting_style#Interleaved_style

  List information: http://vger.kernel.org/majordomo-info.html

* Reply using the --to, --cc, and --in-reply-to
  switches of git-send-email(1):

  git send-email \
    --in-reply-to=b9bd0c2e-63fc-5658-7a24-b8ab078acd44@gmail.com \
    --to=stolee@gmail.com \
    --cc=git@vger.kernel.org \
    --cc=gitgitgadget@gmail.com \
    --cc=gitster@pobox.com \
    --cc=jeffhost@microsoft.com \
    --cc=jonathantanmy@google.com \
    --cc=me@ttaylorr.com \
    --cc=peff@peff.net \
    --cc=szeder.dev@gmail.com \
    /path/to/YOUR_REPLY

  https://kernel.org/pub/software/scm/git/docs/git-send-email.html

* If your mail client supports setting the In-Reply-To header
  via mailto: links, try the mailto: link

git@vger.kernel.org list mirror (unofficial, one of many)

Archives are clonable:
	git clone --mirror https://public-inbox.org/git
	git clone --mirror http://ou63pmih66umazou.onion/git
	git clone --mirror http://czquwvybam4bgbro.onion/git
	git clone --mirror http://hjrcffqmbrq6wope.onion/git

Example config snippet for mirrors

Newsgroups are available over NNTP:
	nntp://news.public-inbox.org/inbox.comp.version-control.git
	nntp://ou63pmih66umazou.onion/inbox.comp.version-control.git
	nntp://czquwvybam4bgbro.onion/inbox.comp.version-control.git
	nntp://hjrcffqmbrq6wope.onion/inbox.comp.version-control.git
	nntp://news.gmane.io/gmane.comp.version-control.git

 note: .onion URLs require Tor: https://www.torproject.org/

AGPL code for this site: git clone https://public-inbox.org/public-inbox.git