Re: [REPORT] [GSoC - TCG Continuous Benchmarking] [#5] Finding Commits Affecting QEMU Performance

[Ahmed Karaman]

On Tue, Jul 21, 2020 at 1:54 PM Alex Bennée <alex.bennee@linaro.org> wrote:
>
>
> Ahmed Karaman <ahmedkhaledkaraman@gmail.com> writes:
>
> > Hi,
> >
> > The fifth report of the TCG Continuous Benchmarking project concludes
> > a mini-series of three reports that dealt with the performance
> > comparison and analysis of QEMU 5.0 and 5.1-pre-soft-freeze.
> >
> > The report presents a new Python script that utilizes "git bisect" for
> > running a binary search within a specified range of commits to
> > automatically detect the commit causing a performance improvement or
> > degradation.
>
> Excellent stuff.

Thanks for your continued support!

>
> > The new script is then used to find the commit introducing the PowerPC
> > performance degradation as well as that introducing the performance
> > improvement in MIPS. The results obtained for both commits proves the
> > correctness of the conclusions and analyses presented in the two
> > previous reports.
>
> I can certainly envision a mechanism where 0673ec slows things down. I
> wonder if it would come back if instead of inline function calls we
> ended up making concrete flattend versions, e.g.:
>
> bool QEMU_FLATTEN float64_eq(float64 a, float64 b, float_status *s)
> {
>     return float64_compare(a, b, s) == float_relation_equal;
> }
>
> PPC is of course more affected by these changes than others because
> HARDFLOAT never gets a chance to kick in. Looking at the objdump of
> f64_compare there should surely be an opportunity to loose some of the
> branches when looking for a certain test result?

Interesting, I will try to tinker a little bit with the float64
functions and will let you know if I find anything interesting.

>
> >
> > Report link:
> > https://ahmedkrmn.github.io/TCG-Continuous-Benchmarking/Finding-Commits-Affecting-QEMU-Performance/
> >
> > Previous reports:
> > Report 1 - Measuring Basic Performance Metrics of QEMU:
> > https://lists.gnu.org/archive/html/qemu-devel/2020-06/msg06692.html
> > Report 2 - Dissecting QEMU Into Three Main Parts:
> > https://lists.gnu.org/archive/html/qemu-devel/2020-06/msg09441.html
> > Report 3 - QEMU 5.0 and 5.1-pre-soft-freeze Dissect Comparison:
> > https://lists.gnu.org/archive/html/qemu-devel/2020-07/msg01978.html
> > Report 4 - Listing QEMU Helpers and Function Callees:
> > https://lists.gnu.org/archive/html/qemu-devel/2020-07/msg04227.html
> >
> > Best regards,
> > Ahmed Karaman
>
>
> --
> Alex Bennée

Best regards,
Ahmed Karaman