linux-kernel - Re: [PATCH 4/4] optimize and simplify get_cycles

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Message-ID: <20070309095710.GB8922@amd.com>
Date:	Fri, 9 Mar 2007 10:57:10 +0100
From:	"Joerg Roedel" <joerg.roedel@....com>
To:	"Andrew Morton" <akpm@...ux-foundation.org>
cc:	discuss@...-64.org, "Andi Kleen" <ak@...e.de>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 4/4] optimize and simplify get_cycles_sync()

On Tue, Mar 06, 2007 at 04:25:41PM -0800, Andrew Morton wrote:
> On Wed, 28 Feb 2007 15:25:54 +0100
> "Joerg Roedel" <joerg.roedel@....com> wrote:
> 
> > From: Joerg Roedel <joerg.roedel@....com>
> > 
> > This patch simplifies the get_cycles_sync() function by removing the
> > #ifdefs from it. Further it introduces an optimization for AMD
> > processors. There the RDTSCP instruction is used instead of CPUID;RDTSC
> > which is helpfull if the kernel runs as a KVM guest. Running as a guest
> > makes CPUID very expensive because it causes an intercept of the guest.
> 
> Problem:
> 
> http://test.kernel.org/functional/index.html
> 
> lots of builds fell over because their binutils versions don't understand
> rdtscp.
> 
> I don't know how recently rdtscp support was added to binutils, but
> this is likely to be a problem.  Perhaps we can change this patch to
> embed the hex code for that opcode instead?

Ok, I will submit an updated version soon. Thanks for pointing this out.

Joerg

-- 
Joerg Roedel
Operating System Research Center
AMD Saxony LLC & Co. KG


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