linux-kernel - Re: [PATCH 5/5] perf, x86: Prefer RDPMC over RDMSR for reading counters

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Date:	Wed, 6 Jun 2012 07:16:44 -0700
From:	Andi Kleen <ak@...ux.intel.com>
To:	Peter Zijlstra <a.p.zijlstra@...llo.nl>
Cc:	Andi Kleen <andi@...stfloor.org>, linux-kernel@...r.kernel.org,
	eranian@...gle.com
Subject: Re: [PATCH 5/5] perf, x86: Prefer RDPMC over RDMSR for reading
 counters

On Wed, Jun 06, 2012 at 12:46:19PM +0200, Peter Zijlstra wrote:
> On Tue, 2012-06-05 at 17:56 -0700, Andi Kleen wrote:
> > From: Andi Kleen <ak@...ux.intel.com>
> > 
> > RDPMC is much faster than RDMSR for reading performance counters,
> > since it's not serializing.  Use it if possible in the perf handler.
> > 
> > Only tested on Sandy Bridge, so I only enabled it there so far.
> 
> That's just stupid.. I took Vince's patch from a while back.

What do you mean? It's significantly faster to read the counters this
way, because it avoids serialization and other overhead. 

Vince's patch only enabled it for user space I believe, This is for lowering
the kernel PMI handler overhead.

-Andi

-- 
ak@...ux.intel.com -- Speaking for myself only
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