From: Segher Boessenkool <segher@kernel.crashing.org>
To: Michael Ellerman <mpe@ellerman.id.au>
Cc: Cyril Bur <cyrilbur@gmail.com>,
Simon Guo <wei.guo.simon@gmail.com>,
raji@linux.vnet.ibm.com,
"Naveen N. Rao" <naveen.n.rao@linux.vnet.ibm.com>,
David Laight <David.Laight@ACULAB.COM>,
linuxppc-dev@lists.ozlabs.org
Subject: Re: [PATCH v2 2/3] powerpc/64: enhance memcmp() with VMX instruction for long bytes comparision
Date: Tue, 26 Sep 2017 06:26:24 -0500 [thread overview]
Message-ID: <20170926112623.GZ8421@gate.crashing.org> (raw)
In-Reply-To: <87k20mf2fn.fsf@concordia.ellerman.id.au>
On Tue, Sep 26, 2017 at 03:34:36PM +1000, Michael Ellerman wrote:
> Cyril Bur <cyrilbur@gmail.com> writes:
> > This was written for userspace which doesn't have to explicitly enable
> > VMX in order to use it - we need to be smarter in the kernel.
>
> Well the kernel has to do it for them after a trap, which is actually
> even more expensive, so arguably the glibc code should be smarter too
> and the threshold before using VMX should probably be higher than in the
> kernel (to cover the cost of the trap).
A lot of userspace code uses V*X, more and more with newer CPUs and newer
compiler versions. If you already paid the price for using vector
registers you do not need to again :-)
> But I digress :)
Yeah sorry :-)
Segher
next prev parent reply other threads:[~2017-09-26 11:26 UTC|newest]
Thread overview: 18+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-09-20 23:34 [PATCH v2 0/3] powerpc/64: memcmp() optimization wei.guo.simon
2017-09-20 23:34 ` [PATCH v2 1/3] powerpc/64: Align bytes before fall back to .Lshort in powerpc64 memcmp() wei.guo.simon
2017-09-20 23:34 ` [PATCH v2 2/3] powerpc/64: enhance memcmp() with VMX instruction for long bytes comparision wei.guo.simon
2017-09-21 0:54 ` Simon Guo
2017-09-22 14:06 ` Cyril Bur
2017-09-23 21:18 ` Simon Guo
2017-09-25 23:59 ` Cyril Bur
2017-09-26 5:34 ` Michael Ellerman
2017-09-26 11:26 ` Segher Boessenkool [this message]
2017-09-27 3:38 ` Michael Ellerman
2017-09-27 9:27 ` Segher Boessenkool
2017-09-27 9:43 ` David Laight
2017-09-27 18:33 ` Simon Guo
2017-09-28 9:24 ` David Laight
2017-09-27 16:22 ` Simon Guo
2017-09-20 23:34 ` [PATCH v2 3/3] powerpc:selftest update memcmp_64 selftest for VMX implementation wei.guo.simon
2017-09-25 9:30 ` David Laight
2017-09-24 6:19 ` Simon Guo
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