From: Leonardo Sandoval <leonardo.sandoval.gonzalez@linux.intel.com>
To: Alexander Monakov <amonakov@ispras.ru>, "H.J. Lu" <hjl.tools@gmail.com>
Cc: GNU C Library <libc-alpha@sourceware.org>
Subject: Re: [PATCH v2] x86-64: Optimize strcmp/wcscmp with AVX2
Date: Fri, 01 Jun 2018 20:23:00 -0000 [thread overview]
Message-ID: <03bdf89c47880fd0734fc5b82213fc3c98eab372.camel@linux.intel.com> (raw)
In-Reply-To: <alpine.LNX.2.20.13.1806011824140.1892@monopod.intra.ispras.ru>
On Fri, 2018-06-01 at 18:28 +0300, Alexander Monakov wrote:
> On Fri, 1 Jun 2018, H.J. Lu wrote:
> > Please mention strncmp and wcsncmp in commit subject. OK with this
> > change.
>
> Many Intel CPUs reduce operating frequency upon encountering AVX
> code,
> and some have a "spin-up" period when frequency is not yet changed
> and
> AVX code runs at reduced throughput. Thus, why is this change not
> detrimental in practice, doesn't it slow down all code (including
> other
> programs running on the same core) as soon as a program makes a call
> to strcmp?
this is partially true for AVX2 FMA and AVX512. What I am proposing
contains none of the latter instructions, just AVX2 without FMA
instructions.
In the other hand, some microbenchmarks were done to see the benefit of
this effort, which is resumed on the commit description but the
complete picture is here
https://github.com/lsandoval/strcmp-avx2-benchmark/blob/master/string-c
omparison-avx2.png
The above numbers are based on a SkyLake platform.
>
> Alexander
next prev parent reply other threads:[~2018-06-01 20:23 UTC|newest]
Thread overview: 9+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-05-29 18:53 leonardo.sandoval.gonzalez
2018-06-01 14:46 ` H.J. Lu
2018-06-01 15:30 ` Alexander Monakov
2018-06-01 20:23 ` Leonardo Sandoval [this message]
2018-06-02 7:46 ` Alexander Monakov
2018-06-02 11:37 ` Florian Weimer
2018-06-04 14:14 ` Leonardo Sandoval
2018-06-05 10:14 ` Alexander Monakov
2018-06-05 14:02 ` Leonardo Sandoval
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