From: Andi Kleen <andi@firstfloor.org>
To: "H. Peter Anvin" <hpa@zytor.com>
Cc: Andi Kleen <andi@firstfloor.org>, Jan Beulich <JBeulich@suse.com>,
mingo@elte.hu, tglx@linutronix.de, linux-kernel@vger.kernel.org
Subject: Re: x86-64: memset()/memcpy() not fully standards compliant
Date: Fri, 6 Jan 2012 10:49:22 +0100 [thread overview]
Message-ID: <20120106094922.GU11715@one.firstfloor.org> (raw)
In-Reply-To: <4F06566B.8080708@zytor.com>
On Thu, Jan 05, 2012 at 06:03:23PM -0800, H. Peter Anvin wrote:
> On 01/05/2012 05:47 PM, Andi Kleen wrote:
> >>
> >> Is that still true, and do we even use string instructions still on
> >> those old CPUs? Jan's fixes don't introduce any additional delays in
> >> the non-string-instruction paths.
> >
> > Yes various of the CPUs with bugs used string instructions.
> >
>
> Which CPUs are you talking about here?
This was various iterations of K8 and PSC. Early Meroms may also have
had issues (not 100% sure).
>
> >
> > Both string and non string instructions are used on modern CPUs,
> > so making any of that slower is not a good idea.
> >
>
> Obviously not, but I'm perfectly fine turning REP_GOOD off on old broken
> CPUs.
That would be even worse.
You would slow a critical fast path operation down for something
that never happens?!? There were big differences between strings
and the unrolled loop for several.
IMHO it's a war games situation: "the only way to win is not to play"
-Andi
next prev parent reply other threads:[~2012-01-06 9:49 UTC|newest]
Thread overview: 18+ messages / expand[flat|nested] mbox.gz Atom feed top
2012-01-05 14:04 x86-64: memset()/memcpy() not fully standards compliant Jan Beulich
2012-01-05 15:27 ` hpanvin@gmail.com
2012-01-05 18:28 ` Andi Kleen
2012-01-05 23:22 ` H. Peter Anvin
2012-01-06 1:47 ` Andi Kleen
2012-01-06 2:03 ` H. Peter Anvin
2012-01-06 7:22 ` Jan Beulich
2012-01-06 9:49 ` Andi Kleen [this message]
2012-01-06 10:22 ` Jan Beulich
2012-01-06 10:37 ` Andi Kleen
2012-01-06 10:50 ` Jan Beulich
2012-01-06 11:08 ` Andi Kleen
2012-01-06 12:25 ` Jan Beulich
2012-01-06 19:44 ` Andi Kleen
2012-01-06 23:12 ` H. Peter Anvin
2012-01-06 11:08 ` Ingo Molnar
2012-01-06 20:40 ` Valdis.Kletnieks
2012-01-09 8:29 ` Jan Beulich
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