linux-kernel - Re: Fast memcpy patch

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Message-ID: <1322053469.3581.17.camel@lappy>
Date:	Wed, 23 Nov 2011 15:04:29 +0200
From:	Sasha Levin <levinsasha928@...il.com>
To:	"N. Coesel" <nico@...dev.nl>
Cc:	linux-kernel@...r.kernel.org
Subject: Re: Fast memcpy patch

On Wed, 2011-11-23 at 13:51 +0100, N. Coesel wrote:
> Sasha,
> 
> At 13:10 23-11-2011, Sasha Levin wrote:
> >On Wed, 2011-11-23 at 12:25 +0100, N. Coesel wrote:
> > > Dear readers,
> > > I noticed the Linux kernel still uses a byte-by-byte copy method for
> > > memcpy. Since most memory allocations are aligned to the integer size
> > > of a cpu it is often faster to copy by using the CPU's native word
> > > size. The patch below does that. The code is already at work in many
> > > 16 and 32 bit embedded products. It should also work for 64 bit
> > > platforms. So far I only tested 16 and 32 bit platforms.
> >
> >[snip]
> >
> >memcpy (along with other mem* functions) are arch specific - for
> >example, look at arch/x86/lib/memcpy_64.S for the implementation(s) for
> >x86.
> >
> >The code under lib/string.c is simple and should work on all platforms
> >(and is probably not being used anywhere anymore).
> 
> Thanks for pointing that out. Currently my primary target is ARM. It 
> seems the memcpy for that arch uses byte-by-byte copying as well with 
> some loop unrolling. I modified the code so it tries to use 
> word-by-word copy if the pointers are aligned on word boundaries, if 
> not it reverts to the old method. For clarity: by word I mean the 
> CPU's native bus width. In case of ARM that's (still) 32 bit.

I don't think we're looking at the same file.

For arm it's arch/arm/lib/copy_template.S, right? Or are you talking
about something else?

-- 

Sasha.

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