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From: Taylor Blau <me@ttaylorr.com>
To: Derrick Stolee via GitGitGadget <gitgitgadget@gmail.com>
Cc: git@vger.kernel.org, "Michael Haggerty" <mhagger@alum.mit.edu>,
	me@ttaylorr.com, peff@peff.net, gitster@pobox.com,
	"René Scharfe" <l.s.r@web.de>,
	"Derrick Stolee" <stolee@gmail.com>,
	"Derrick Stolee" <derrickstolee@github.com>,
	"Derrick Stolee" <dstolee@microsoft.com>
Subject: Re: [PATCH v2 5/5] commit-reach: stale commits may prune generation further
Date: Wed, 3 Feb 2021 10:59:05 -0500	[thread overview]
Message-ID: <YBrISQ/5/pJKgGGZ@nand.local> (raw)
In-Reply-To: <14f0974c987215bd36e91450c1a6ebc6d5732121.1612183647.git.gitgitgadget@gmail.com>

On Mon, Feb 01, 2021 at 12:47:27PM +0000, Derrick Stolee via GitGitGadget wrote:
> From: Derrick Stolee <dstolee@microsoft.com>
> Note that these are only modest improvements for the case where the two
> independent commits are not in the commit-graph (not until v5.10). All
> algorithms get faster as more commits are indexed, which is not a
> surprise. However, the cost of walking extra commits is more and more
> prevalent in relative terms as more commits are indexed. Finally, the
> last case allows us to jump to the minimum generation between the last
> two commits (that are actually independent) so we greatly reduce the
> cost in that case.

Very nice. The explanation and implementation makes sense to me.

> Signed-off-by: Derrick Stolee <dstolee@microsoft.com>
> ---
>  commit-reach.c | 28 +++++++++++++++++++++-------
>  1 file changed, 21 insertions(+), 7 deletions(-)
>
> diff --git a/commit-reach.c b/commit-reach.c
> index d3a6e2bdd04..c2e0747fea4 100644
> --- a/commit-reach.c
> +++ b/commit-reach.c
> @@ -237,15 +237,27 @@ static int remove_redundant_with_gen(struct repository *r,
>  {
>  	int i, count_non_stale = 0, count_still_independent = cnt;
>  	timestamp_t min_generation = GENERATION_NUMBER_INFINITY;
> -	struct commit **walk_start;
> +	struct commit **walk_start, **sorted;
>  	size_t walk_start_nr = 0, walk_start_alloc = cnt;
> +	int min_gen_pos = 0;
> +
> +	/*
> +	 * Sort the input by generation number, ascending. This allows
> +	 * us to increase the "min_generation" limit when we discover
> +	 * the commit with lowest generation is STALE. The index
> +	 * min_gen_pos points to the current position within 'array'
> +	 * that is not yet known to be STALE.
> +	 */
> +	ALLOC_ARRAY(sorted, cnt);
> +	COPY_ARRAY(sorted, array, cnt);
> +	QSORT(sorted, cnt, compare_commits_by_gen);
> +	min_generation = commit_graph_generation(sorted[0]);

This line caught my eye, but we return early in
commit-reach.c:reduce_heads() before even calling remove_redundant()
(which itself calls remove_redundant_with_gen()), so it's always OK to
assume that we have at least one element in 'array'.

This patch and the others in v2 all look good to me.

Thanks,
Taylor

  reply	other threads:[~2021-02-03 16:02 UTC|newest]

Thread overview: 36+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-01-28 16:24 [PATCH 0/3] Speed up remove_redundant() Derrick Stolee via GitGitGadget
2021-01-28 16:24 ` [PATCH 1/3] commit-reach: use one walk in remove_redundant() Derrick Stolee via GitGitGadget
2021-01-28 20:51   ` Junio C Hamano
2021-01-29 17:11     ` René Scharfe
2021-01-31  3:52       ` Derrick Stolee
2021-01-31 10:20         ` René Scharfe
2021-01-31  3:59     ` Derrick Stolee
2021-01-31 20:13       ` Derrick Stolee
2021-01-31 20:25       ` Junio C Hamano
2021-02-01  3:55         ` Derrick Stolee
2021-01-29 17:10   ` René Scharfe
2021-01-28 16:24 ` [PATCH 2/3] commit-reach: move compare_commits_by_gen Derrick Stolee via GitGitGadget
2021-01-28 16:24 ` [PATCH 3/3] commit-reach: use heuristic in remove_redundant() Derrick Stolee via GitGitGadget
2021-01-28 20:20 ` [PATCH 0/3] Speed up remove_redundant() Junio C Hamano
2021-02-01 12:47 ` [PATCH v2 0/5] " Derrick Stolee via GitGitGadget
2021-02-01 12:47   ` [PATCH v2 1/5] commit-reach: reduce requirements for remove_redundant() Derrick Stolee via GitGitGadget
2021-02-01 19:51     ` Junio C Hamano
2021-02-01 12:47   ` [PATCH v2 2/5] commit-reach: use one walk in remove_redundant() Derrick Stolee via GitGitGadget
2021-02-01 16:12     ` René Scharfe.
2021-02-01 16:31       ` Derrick Stolee
2021-02-01 12:47   ` [PATCH v2 3/5] commit-reach: move compare_commits_by_gen Derrick Stolee via GitGitGadget
2021-02-01 12:47   ` [PATCH v2 4/5] commit-reach: use heuristic in remove_redundant() Derrick Stolee via GitGitGadget
2021-02-01 20:05     ` Junio C Hamano
2021-02-01 21:02       ` Derrick Stolee
2021-02-01 12:47   ` [PATCH v2 5/5] commit-reach: stale commits may prune generation further Derrick Stolee via GitGitGadget
2021-02-03 15:59     ` Taylor Blau [this message]
2021-02-01 15:48   ` [PATCH v2 0/5] Speed up remove_redundant() Derrick Stolee
2021-02-18 23:25     ` Junio C Hamano
2021-02-19 12:17       ` Derrick Stolee
2021-02-20  3:32         ` Junio C Hamano
2021-02-19 12:34   ` [PATCH v3 " Derrick Stolee via GitGitGadget
2021-02-19 12:34     ` [PATCH v3 1/5] commit-reach: reduce requirements for remove_redundant() Derrick Stolee via GitGitGadget
2021-02-19 12:34     ` [PATCH v3 2/5] commit-reach: use one walk in remove_redundant() Derrick Stolee via GitGitGadget
2021-02-19 12:34     ` [PATCH v3 3/5] commit-reach: move compare_commits_by_gen Derrick Stolee via GitGitGadget
2021-02-19 12:34     ` [PATCH v3 4/5] commit-reach: use heuristic in remove_redundant() Derrick Stolee via GitGitGadget
2021-02-19 12:34     ` [PATCH v3 5/5] commit-reach: stale commits may prune generation further Derrick Stolee via GitGitGadget

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