From: Simon Guo <wei.guo.simon@gmail.com>
To: David Laight <David.Laight@ACULAB.COM>
Cc: "linuxppc-dev@lists.ozlabs.org" <linuxppc-dev@lists.ozlabs.org>,
"Naveen N. Rao" <naveen.n.rao@linux.vnet.ibm.com>
Subject: Re: [PATCH v1 1/3] powerpc: Align bytes before fall back to .Lshort in powerpc memcmp
Date: Wed, 20 Sep 2017 17:56:35 +0800 [thread overview]
Message-ID: <20170920095635.GA3387@simonLocalRHEL7.x64> (raw)
In-Reply-To: <063D6719AE5E284EB5DD2968C1650D6DD0079D63@AcuExch.aculab.com>
On Tue, Sep 19, 2017 at 10:12:50AM +0000, David Laight wrote:
> From: wei.guo.simon@gmail.com
> > Sent: 19 September 2017 11:04
> > Currently memcmp() in powerpc will fall back to .Lshort (compare per byte
> > mode) if either src or dst address is not 8 bytes aligned. It can be
> > opmitized if both addresses are with the same offset with 8 bytes boundary.
> >
> > memcmp() can align the src/dst address with 8 bytes firstly and then
> > compare with .Llong mode.
>
> Why not mask both addresses with ~7 and mask/shift the read value to ignore
> the unwanted high (BE) or low (LE) bits.
>
> The same can be done at the end of the compare with any final, partial word.
>
> David
>
Yes. That will be better. A prototyping shows ~5% improvement on 32 bytes
size comparison with v1. I will rework on v2.
Thanks for the suggestion.
BR,
- Simon
next prev parent reply other threads:[~2017-09-20 9:56 UTC|newest]
Thread overview: 10+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-09-19 10:03 [PATCH v1 0/3] powerpc: memcmp() optimization wei.guo.simon
2017-09-19 10:03 ` [PATCH v1 1/3] powerpc: Align bytes before fall back to .Lshort in powerpc memcmp wei.guo.simon
2017-09-19 10:12 ` David Laight
2017-09-20 9:56 ` Simon Guo [this message]
2017-09-20 10:05 ` David Laight
2017-09-19 12:20 ` Christophe LEROY
2017-09-19 10:03 ` [PATCH v1 2/3] powerpc: enhance memcmp() with VMX instruction for long bytes comparision wei.guo.simon
2017-09-19 10:03 ` [PATCH v1 3/3] powerpc:selftest update memcmp selftest according to kernel change wei.guo.simon
2017-09-19 12:21 ` [PATCH v1 0/3] powerpc: memcmp() optimization Christophe LEROY
2017-09-20 9:57 ` Simon Guo
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