From: "H.J. Lu" <hjl.tools@gmail.com>
To: Florian Weimer <fweimer@redhat.com>
Cc: "H.J. Lu via Libc-alpha" <libc-alpha@sourceware.org>,
Arjan van de Ven <arjan@linux.intel.com>,
liuhongt <hongtao.liu@intel.com>,
Thiago Macieira <thiago.macieira@intel.com>,
Hongyu Wang <hongyu.wang@intel.com>
Subject: Re: [PATCH] x86: Don't set Prefer_No_AVX512 for processors with AVX512 and AVX-VNNI
Date: Tue, 7 Dec 2021 07:52:44 -0800 [thread overview]
Message-ID: <CAMe9rOoZVBuTaT9XmmBZs-KUFFrNOw3R0_nroUH7n9JJe_J5nQ@mail.gmail.com> (raw)
In-Reply-To: <878rwwquvk.fsf@oldenburg.str.redhat.com>
On Tue, Dec 7, 2021 at 7:48 AM Florian Weimer <fweimer@redhat.com> wrote:
>
> * H. J. Lu via Libc-alpha:
>
> > On Tue, Dec 7, 2021 at 6:05 AM Florian Weimer <fweimer@redhat.com> wrote:
> >>
> >> * H. J. Lu via Libc-alpha:
> >>
> >> > Hongtao, Hongyu, can you find a Rocket Lake to test?
> >>
> >> I've found a lab machine with an i7-11700 CPU. Is there something I
> >> could test for you?
> >
> > You can enable AVX512 in glibc with:
> >
> > $ export GLIBC_TUNABLES=glibc.cpu.hwcaps=-Prefer_No_AVX512
> >
> > While bootstrapping GCC with -j8, track CPU frequency with turbostat. If
> > there is no CPU frequency drop and build time is less comparing against
> > without GLIBC_TUNABLES, we can enable AVX512.
> >
> >> (This could be non-production silicon, though.)
> >>
> >
> > The frequency behavior of non-production silicon can be different.
>
> With that caveat, it seems that frequencies drop further with
> GLIBC_TUNABLES set as above, and the build is also a little bit slower
> (5m31s vs 5m23s, the AVX-512 build was run first, and the systems was a
> little bit warmer for the second run).
>
> Would it make sense to run more extensive tests, or should we wait for
> someone with production silicon to show up?
GCC is a heavy user of memcpy/memset, which is a good proxy of
ZMM load/store impact on CPU frequency. We need to run the same
test on a production Rocket Lake.
--
H.J.
next prev parent reply other threads:[~2021-12-07 15:53 UTC|newest]
Thread overview: 12+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-12-06 3:23 H.J. Lu
2021-12-07 7:47 ` Noah Goldstein
2021-12-07 12:53 ` H.J. Lu
2021-12-07 13:17 ` Arjan van de Ven
2021-12-07 13:34 ` H.J. Lu
2021-12-07 14:05 ` Florian Weimer
2021-12-07 14:15 ` H.J. Lu
2021-12-07 15:47 ` Florian Weimer
2021-12-07 15:52 ` H.J. Lu [this message]
2021-12-07 16:22 ` Thiago Macieira
2021-12-07 19:32 ` Noah Goldstein
2022-04-23 1:51 ` Sunil Pandey
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