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

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Message-ID: <20120221033231.GA3776@phenom.dumpdata.com>
Date:	Mon, 20 Feb 2012 22:32:31 -0500
From:	Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>
To:	Steven Rostedt <rostedt@...dmis.org>
Cc:	tglx@...utronix.de, mingo@...hat.com, hpa@...or.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).

On Mon, Feb 20, 2012 at 08:01:43PM -0500, Steven Rostedt 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?

No. I hadn't realized that flag existed until your email a couple of days ago - I hadn't
had a chance to see if the notrace would solve this. But let me do that and get
back on this.
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