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Date:	Mon, 9 Apr 2007 09:40:29 -0700
From:	William Lee Irwin III <wli@...omorphy.com>
To:	Christoph Lameter <clameter@....com>
Cc:	Andy Whitcroft <apw@...dowen.org>,
	Martin Bligh <mbligh@...gle.com>,
	Dave Hansen <hansendc@...ibm.com>, Andi Kleen <ak@...e.de>,
	linux-kernel@...r.kernel.org, linux-arch@...r.kernel.org,
	linux-mm@...ck.org,
	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
Subject: Re: [PATCH 1/4] x86_64: (SPARSE_VIRTUAL doubles sparsemem speed)

On Sat, Apr 07, 2007 at 03:06:13PM -0700, Christoph Lameter wrote:
> +/*
> + * Performance Counters and Measurement macros
> + * (C) 2005 Silicon Graphics Incorporated
> + * by Christoph Lameter <clameter@....com>, April 2005
> + *
> + * Counters are calculated using the cycle counter. If a process
> + * is migrated to another cpu during the measurement then the measurement
> + * is invalid.
> + *
> + * We cannot disable preemption during measurement since that may interfere
> + * with other things in the kernel and limit the usefulness of the counters.
> + */

Whatever's going on with the rest of this, I really like this
instrumentation patch. It may be worthwhile to allow pc_start() to be
overridden so things like performance counter MSR's are usable, but
the framework looks very useful.


-- wli
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