Re: [GSoC] Git Blog 11

From: Christian Couder <christian.couder@gmail.com>
Date: Aug 4, 2021, 08:56 UTC
Message-ID: <CAP8UFD3E9oR9E4S=f8iReKOnvVO_WrXVziyztHZJCiScUAxDRg@mail.gmail.com>
In-Reply-To: <CAOLTT8QDo1A4tRqU0w-yas8OxrHB6uQ_PECswUQtQ7yY2-iWgw@mail.gmail.com>

On Tue, Aug 3, 2021 at 4:48 AM ZheNing Hu <adlternative@gmail.com> wrote:

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>
> ZheNing Hu <adlternative@gmail.com> 于2021年8月3日周二 上午10:37写道：
> >
> > Christian Couder <christian.couder@gmail.com> 于2021年8月2日周一 下午2:25写道：
> > >
> > > On Sun, Aug 1, 2021 at 8:45 AM ZheNing Hu <adlternative@gmail.com> wrote:
> > >
> > > > in some cases, this is the result of the performance test of
> > > > `t/perf/p1006-cat-file.sh`:
> > > >
> > > > ```
> > > > Test                                        HEAD~             HEAD
> > > > ------------------------------------------------------------------------------------
> > > > 1006.2: cat-file --batch-check              0.10(0.09+0.00)
> > > > 0.11(0.10+0.00) +10.0%
> > > > 1006.3: cat-file --batch-check with atoms   0.09(0.08+0.01)
> > > > 0.09(0.06+0.03) +0.0%
> > > > 1006.4: cat-file --batch                    0.62(0.58+0.04)
> > > > 0.57(0.54+0.03) -8.1%
> > > > 1006.5: cat-file --batch with atoms         0.63(0.60+0.02)
> > > > 0.52(0.49+0.02) -17.5%
> > > > ```
> > > >
> > > > We can see that the performance of `git cat-file --batch` has been a
> > > > certain improvement!
> > >
> > > Yeah, sure -8.1% or -17.5% is really nice! But why +10.0% for
> > > `cat-file --batch-check`?
> >
> > I think it's not very important. Because our optimization is skipping
> > parse_object_buffer(), git cat-file --batch-check will not set oi->contentp
> > by default, parse_object_buffer() will not be executed.

Do you think that if git cat-file --batch-check would set oi->contentp, there would be no performance regression for `cat-file --batch-check`? Could you test that?

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> > Therefore, we did
> > not optimize `git cat-file --batch-check` at all. 10% may be small enough
> > for git cat-file --batch-check. The noise of environment even will cover it...
>
> By the way, its performance may still be worse than "upstream/master", but it
> will be better than before optimization.

Nice that there is some improvement, but it would be better if it was similar to "upstream/master".

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> Test                                        HEAD~             this tree
> ------------------------------------------------------------------------------------
> 1006.2: cat-file --batch-check              0.10(0.09+0.01)
> 0.09(0.08+0.01) -10.0%
> 1006.3: cat-file --batch-check with atoms   0.09(0.07+0.02)
> 0.08(0.05+0.03) -11.1%
> 1006.4: cat-file --batch                    0.61(0.59+0.02)
> 0.53(0.51+0.02) -13.1%
> 1006.5: cat-file --batch with atoms         0.60(0.57+0.02)
> 0.52(0.49+0.03) -13.3%

Yeah, your patch seems to be an overall improvement when the ref-filter code is used.

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> Test                                        upstream/master   this
> tree
> ------------------------------------------------------------------------------------
> 1006.2: cat-file --batch-check              0.08(0.07+0.01)
> 0.10(0.07+0.02) +25.0%
> 1006.3: cat-file --batch-check with atoms   0.06(0.05+0.01)
> 0.08(0.08+0.00) +33.3%
> 1006.4: cat-file --batch                    0.49(0.46+0.03)
> 0.53(0.50+0.03) +8.2%
> 1006.5: cat-file --batch with atoms         0.48(0.45+0.03)
> 0.51(0.48+0.02) +6.3%

This means that some further performance improvements are still needed both for --batch and --batch-check though.

Have you tried to see, using gprof or something else, what is still degrading the performance compared to when the ref-filter code isn't used?