From: Tay Ray Chuan <rctay89@gmail.com>
To: Junio C Hamano <gitster@pobox.com>
Cc: Git Mailing List <git@vger.kernel.org>,
"Shawn O. Pearce" <spearce@spearce.org>
Subject: Re: [RFC/PATCH 1/3] teach --histogram to diff
Date: Thu, 14 Jul 2011 00:36:18 +0800 [thread overview]
Message-ID: <CALUzUxqv5PTche5-fG5CPVg+hrO1a0R73gF23gcJbWM3wO_wbA@mail.gmail.com> (raw)
In-Reply-To: <7vy6036zon.fsf@alter.siamese.dyndns.org>
On Wed, Jul 13, 2011 at 3:56 AM, Junio C Hamano <gitster@pobox.com> wrote:
> This is just half-a-review (bottom half of the file).
> [snip]
>> + result = histogram_diff(xpp, env,
>> + line1, lcs.begin1 - line1,
>> + line2, lcs.begin2 - line2);
>> + result = histogram_diff(xpp, env,
>> + lcs.end1 + 1, LINE_END(1) - lcs.end1,
>> + lcs.end2 + 1, LINE_END(2) - lcs.end2);
>
> The result from the first half before lcs is discarded?
>
>> + result *= -1;
>
> Again, what does this function (called recursively) return, and what does
> flipping the sign of it do?
Oops, my bad.
>[snip]
>> + reduce_common_start_end(xpp, env, &line1, &count1, &line2, &count2);
>
> What this does is logically not specific to histogram algorithm but can be
> applied to other backends, no? And I vaguely recall that Linus did try
> something like this once, found some issues with it when context is set to
> non zero, and stopped doing it (sorry, I do not have any more details).
>
> I am not suggesting you to remove this call or hoist the call to one level
> up to xdl_do_diff(), but I do have to wonder how much of the performance
> improvement you reported is due to this common head/tail reduction.
I believe xdiff already performs this for the Meyers algorithm (in
xprepare.c:xdl_trim_ends()), but the Meyers code doesn't look like it
uses this information at all. If this is the case, then I do think
that a large part of the performance improvement is due to this common
reduction - for git log -p, one would expect a pretty large number of
common head/tail lines in files within a commit.
--
Cheers,
Ray Chuan
next prev parent reply other threads:[~2011-07-13 16:36 UTC|newest]
Thread overview: 24+ messages / expand[flat|nested] mbox.gz Atom feed top
2011-07-12 6:10 [RFC/PATCH 0/3] teach --histogram to diff Tay Ray Chuan
2011-07-12 6:10 ` [RFC/PATCH 1/3] " Tay Ray Chuan
2011-07-12 6:10 ` [RFC/PATCH 2/3] xdiff/xprepare: skip classification Tay Ray Chuan
2011-07-12 6:10 ` [RFC/PATCH 3/3] xdiff/xprepare: use a smaller sample size for histogram diff Tay Ray Chuan
2011-07-12 19:56 ` [RFC/PATCH 1/3] teach --histogram to diff Junio C Hamano
2011-07-13 16:36 ` Tay Ray Chuan [this message]
2011-07-12 14:19 ` [RFC/PATCH 0/3] " Shawn Pearce
2011-07-12 17:43 ` Junio C Hamano
2011-07-13 16:35 ` Tay Ray Chuan
2011-07-13 16:34 ` Tay Ray Chuan
2011-08-01 3:16 ` [PATCH v2 0/8] " Tay Ray Chuan
2011-08-01 3:16 ` [PATCH v2 1/8] xdiff/xprepare: use memset() Tay Ray Chuan
2011-08-01 3:16 ` [PATCH v2 2/8] do away with xdl_mmfile_next() Tay Ray Chuan
2011-08-01 3:16 ` [PATCH v2 3/8] xdiff/xprepare: refactor abort cleanups Tay Ray Chuan
2011-08-01 3:16 ` [PATCH v2 4/8] xdiff/xpatience: factor out fall-back-diff function Tay Ray Chuan
2011-08-01 3:16 ` [PATCH v2 5/8] t4033-diff-patience: factor out tests Tay Ray Chuan
2011-08-01 3:16 ` [PATCH v2 6/8] teach --histogram to diff Tay Ray Chuan
2011-08-01 3:16 ` [PATCH v2 7/8] xdiff/xprepare: skip classification Tay Ray Chuan
2011-08-01 3:16 ` [PATCH v2 8/8] xdiff/xprepare: use a smaller sample size for histogram diff Tay Ray Chuan
2011-08-01 4:20 ` [PATCH 0/4] changes for rc/histogram-diff in 'next' Tay Ray Chuan
2011-08-01 4:20 ` [PATCH 1/4] xdiff: do away with xdl_mmfile_next() Tay Ray Chuan
2011-08-01 4:20 ` [PATCH 2/4] xdiff/xhistogram: rework handling of recursed results Tay Ray Chuan
2011-08-01 4:20 ` [PATCH 3/4] xdiff/xhistogram: rely on xdl_trim_ends() Tay Ray Chuan
2011-08-01 4:20 ` [PATCH 4/4] xdiff/xhistogram: drop need for additional variable Tay Ray Chuan
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