linux-kernel - Re: [PATCH] i386: optimize memset of 6 and 8 bytes

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Message-ID: <20070817203139.61d1505b@freepuppy.rosehill.hemminger.net>
Date:	Fri, 17 Aug 2007 20:31:39 -0700
From:	Stephen Hemminger <shemminger@...ux-foundation.org>
To:	Arjan van de Ven <arjan@...radead.org>
Cc:	"David S. Miller" <davem@...emloft.net>,
	Andrew Morton <akpm@...ux-foundation.org>,
	linux-kernel@...r.kernel.org, netdev@...r.kernel.org
Subject: Re: [PATCH] i386: optimize memset of 6 and 8 bytes

On Fri, 17 Aug 2007 18:57:00 -0700
Arjan van de Ven <arjan@...radead.org> wrote:

> 
> On Fri, 2007-08-17 at 18:54 -0700, Stephen Hemminger wrote:
> > On Fri, 17 Aug 2007 18:49:34 -0700
> > Arjan van de Ven <arjan@...radead.org> wrote:
> > 
> > > 
> > > On Fri, 2007-08-17 at 16:50 -0700, Stephen Hemminger wrote:
> > > > Tne network code does memset for 6 and 8 byte values, that can easily
> > > > be optimized into simple assignments without string instructions.
> > > 
> > > 
> > > so... question.
> > > Why are we doing this by hand? Wouldn't gcc just generate this code in
> > > the first place (when using __builtin_memset)? I very much suspect it
> > > would (and if some version doesn't.... we really ought to get that
> > > fixed)
> > 
> > i386 and x86_64 are not using __builtin_memset, as least from the
> > code that I see generated.
> 
> .. maybe we should just fix it that way then?
> 
There probably is history behind the decision, like gcc problems
on some old compiler version.

-- 
Stephen Hemminger <shemminger@...ux-foundation.org>
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