linux-kernel - Re: x86-64: memset()/memcpy() not fully standards compliant

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Date:	Fri, 06 Jan 2012 07:22:34 +0000
From:	"Jan Beulich" <JBeulich@...e.com>
To:	"Andi Kleen" <andi@...stfloor.org>,
	"H. Peter Anvin" <hpa@...or.com>
Cc:	<mingo@...e.hu>, <tglx@...utronix.de>,
	<linux-kernel@...r.kernel.org>
Subject: Re: x86-64: memset()/memcpy() not fully standards compliant

>>> On 06.01.12 at 03:03, "H. Peter Anvin" <hpa@...or.com> 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?

Indeed, I went through various specification updates/revision guides
without finding any relevant erratum.

>> 
>> 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.

Yes, that's what my plan would have been too, had I been able to
identify any specific CPU(s) that actually suffer from such problems.

Jan

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