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Re: Branching for 1.3: blame speedup

From: Julian Foad <julianfoad_at_btopenworld.com>
Date: 2005-09-25 00:57:54 CEST

Daniel Berlin wrote:
> On Fri, 2005-09-23 at 07:40 -0400, C. Michael Pilato wrote:
>>kfogel@collab.net writes:
>>>"Peter N. Lundblad" <peter@famlundblad.se> writes:
>>>
>>>>HOw about the remaining blame optimizations (dberlin?)? I'm talking about
>>>>the reversal of the revision fetching.
>>>
>>I, too, am interested in the relationship between the blame speedups
>>and issue #1970. Besides the obvious improvement of the initial
>>get-locations call that precedes the real annotation work,
>
>
> At least for GCC, this was where most of the slowdown was.
>
> For files like ChangeLog, which had 50k revisions, it spent 10-20
> minutes doing the get-locations and 3 minutes doing the blame. It would
> send nothing during get-locations, and was not ctrl-c'able.
>
> Reverse blaming sped this up in part because it was streamy (IE it would
> send during get-locations), so the times of doing blame vs get-locations
> overlapped, causing a speedup. It was also more responsive.
>
> It was also just faster, which gave you about a 15% speedup in blaming
> on most files.
>
> Other than that, the only case the new blame will *really* help is if
> your files can be blamed in less than the number of revisions you've
> asked for (ChangeLog could). This requires a nice way to tell the
> server you are finished blaming before it's finished sending revisions.
>
> Considering all the algorithmic complexity, etc, it seemed hardly worth
> it at that point for a 15% speedup. 3 minutes vs 2 minutes 45 seconds
> is not interesting :).
>
> Both blame algorithms are diff bound, and there are some obvious
> hotspots in diff (IE things that profiling shows taking >30% of the
> time). Thus, IMHO, it makes a lot more sense to work on diff's speed
> now that 1970 is fixed, than introduce a lot of complex code for a 15%
> speedup on blaming most files.
>
> All of this is why i stopped working on blame once patches for 1970
> started becoming available (IE when Greg attached his first closest copy
> patch that only worked on FSFS). It reduced the blame time for files on
> gcc that have been around a while from 15-25 minutes to 2 or 3.

Perhaps someone could add this useful summary in a suitable permanent place -
such as an issue about blame speed-ups?

- Julian

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Received on Sun Sep 25 00:58:51 2005

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