x86-64: strlen-evex performance performance degradation compared to strlen-avx2

[Sunil Pandey]

On Sun, Apr 28, 2024 at 9:17 AM H.J. Lu <hjl.tools@gmail.com> wrote:

> On Sun, Apr 28, 2024 at 9:13 AM Sunil Pandey <skpgkp2@gmail.com> wrote:
> >
> >
> >
> > On Sat, Apr 27, 2024 at 7:13 PM abush wang <abushwangs@gmail.com> wrote:
> >>
> >> Actually, I was handling performance issue from  libmicro in our distro
> OS.
> >> I found that the performance degradation of localtime_r benchmark from
> libmicro is blame to strlen.
> >> So I abstracted this test case.
> >>
> >
> > Can you consistently reproduce strlen perf behaviour by running multiple
> times back-to-back?
> >
> > You can see high swing from run
>
> Hi Sunil,
>
> Intel(R) Xeon(R) Gold 6133 CPU @ 2.50GHz is SKX.  Please add this test to
> benchtests/bench-strlen.c and check its performance on SKX.
>
> --
> H.J.
>

I collected the glibc micro-benchmark data for the string length in
question.

2.38 evex data:

length=4, alignment=4:         4.40
length=4, alignment=0:         4.29
length=4, alignment=0:         3.64
length=4, alignment=7:         3.64
length=4, alignment=2:         3.64

2.28 evex data:

Length    4, alignment  4: 6.46875
Length    4, alignment  0: 6.5
Length    4, alignment  0: 6.53125
Length    4, alignment  7: 6.46875
Length    4, alignment  2: 6.53125

Data collected on Machine: Intel(R) Xeon(R) Gold 6148 CPU @ 2.40GHz

2.38 perf numbers are better than 2.28 as expected.

--Sunil
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