linux-kernel - Re: [PATCH 3/4] perf, x86: Use ALTERNATIVE() to check for X86_FEATURE_PERFCTR

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Message-ID: <20110419103927.GV31407@erda.amd.com>
Date:	Tue, 19 Apr 2011 12:39:27 +0200
From:	Robert Richter <robert.richter@....com>
To:	Andi Kleen <andi@...stfloor.org>
CC:	Peter Zijlstra <peterz@...radead.org>, Ingo Molnar <mingo@...e.hu>,
	Stephane Eranian <eranian@...gle.com>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 3/4] perf, x86: Use ALTERNATIVE() to check for
 X86_FEATURE_PERFCTR_CORE

On 18.04.11 16:00:57, Andi Kleen wrote:
> Robert Richter <robert.richter@....com> writes:
> 
> > Using ALTERNATIVE() when checking for X86_FEATURE_PERFCTR_CORE avoids
> > an extra pointer chase and data cache hit.
> 
> Is that really a performance critical path?
> 
> Seems more like unnecessary obfuscation to me.

We hotest path is in perf_pmu_disable(), which happens at least with
every task switch when calling the event scheduler.

-Robert

-- 
Advanced Micro Devices, Inc.
Operating System Research Center

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