linux-kernel - Re: [PATCH] x86 fixes for 3.3 impacting distros (v1).

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Date:	Mon, 20 Feb 2012 17:38:52 -0800
From:	"H. Peter Anvin" <hpa@...or.com>
To:	Steven Rostedt <rostedt@...dmis.org>,
	Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>
CC:	tglx@...utronix.de, mingo@...hat.com, x86@...nel.org,
	linux-kernel@...r.kernel.org, xen-devel@...ts.xensource.com
Subject: Re: [PATCH] x86 fixes for 3.3 impacting distros (v1).

Odd... given that that is the NOP recommended by AMD.

Steven Rostedt <rostedt@...dmis.org> wrote:

>On Fri, 2012-02-10 at 10:34 -0500, Konrad Rzeszutek Wilk wrote:
>>    66 66 66 90          	data32 data32 xchg %ax,%ax
>> 
>> [the 66 66 .. is 'nop']. Looks good right? Well, it does work very
>well on Intel
>> (used an i3 2100), but on AMD A8-3850 it hits a performance wall -
>that I found out
>> is a result of CONFIG_FUNCTION_TRACER (too many nops??) being
>compiled in (but the tracer
>> is set to the default 'nop'). If I disable that specific config
>option the numbers
>> are the same as the baseline (with CONFIG_FUNCTION_TRACER disabled)
>on the AMD box.
>> Interestingly enough I only see these on AMD machines - not on the
>Intel ones.
>
>All paravirt ops should be labeled with "notrace" so that function
>tracer does not trace those functions. Have you annotated your new
>paravirt ops with notrace?
>
>-- Steve

-- 
Sent from my mobile phone. Please excuse my brevity and lack of formatting.
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