From: "Senkevich, Andrew" <andrew.senkevich@intel.com>
To: "H.J. Lu" <hjl.tools@gmail.com>
Cc: GNU C Library <libc-alpha@sourceware.org>
Subject: RE: [PATCH] x86: Add MathVec_Prefer_No_AVX512 to cpu-features [BZ #21967]
Date: Tue, 12 Sep 2017 14:27:00 -0000 [thread overview]
Message-ID: <D373487E0338A646909492FF43BA8BE356BAA216@irsmsx110.ger.corp.intel.com> (raw)
In-Reply-To: <CAMe9rOrOg8ZDpPG94s51xmVVLLnye1gDXOZLxjaSt6t49jfqzw@mail.gmail.com>
> -----Original Message-----
> From: H.J. Lu [mailto:hjl.tools@gmail.com]
> Sent: Monday, September 4, 2017 22:27
> To: Senkevich, Andrew <andrew.senkevich@intel.com>
> Cc: GNU C Library <libc-alpha@sourceware.org>
> Subject: Re: [PATCH] x86: Add MathVec_Prefer_No_AVX512 to cpu-features [BZ
> #21967]
>
> On Mon, Sep 4, 2017 at 3:16 AM, Senkevich, Andrew
> <andrew.senkevich@intel.com> wrote:
> >> -----Original Message-----
> >> From: Lu, Hongjiu
> >> Sent: Friday, September 1, 2017 19:41
> >> To: GNU C Library <libc-alpha@sourceware.org>
> >> Cc: Senkevich, Andrew <andrew.senkevich@intel.com>
> >> Subject: [PATCH] x86: Add MathVec_Prefer_No_AVX512 to cpu-features
> >> [BZ #21967]
> >>
> >> AVX512 functions in mathvec are used on machines with AVX512. An
> >> AVX2 wrapper is also provided and it can be used when the AVX512
> >> version isn't profitable. MathVec_Prefer_No_AVX512 is addded to cpu-
> features.
> >> If glibc.tune.hwcaps=MathVec_Prefer_No_AVX512 is set in
> >> GLIBC_TUNABLES environment variable, the AVX2 wrapper will be used.
> >>
> >> Tested on x86-64 machines with and without AVX512. Also verified
> >> glibc.tune.hwcaps=MathVec_Prefer_No_AVX512 on AVX512 machine.
> >>
> >> Any comments?
> >
> > But libc selects AVX2 mem/str on SKX, looks like libmvec should do the same
> (and backward option MathVec_Prefer_AVX512 needed).
> >
>
> AVX2 mem/str can be called from codes which may use only SSE or AVX. But
> AVX512 functions in mathvec are called only from AVX512 programs. Do we
> have benchmarks to show that AVX512 programs are faster with AVX2 mathvec?
I agree, if compiler vectorizes with AVX512 then Glibc should use AVX512 implementations in mathvec by default.
--
Andrew
next prev parent reply other threads:[~2017-09-12 14:27 UTC|newest]
Thread overview: 5+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-09-01 17:40 H.J. Lu
2017-09-04 10:16 ` Senkevich, Andrew
2017-09-04 20:27 ` H.J. Lu
2017-09-12 14:27 ` Senkevich, Andrew [this message]
2017-09-12 14:43 ` H.J. Lu
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