linux-kernel - Re: [RFC][PATCH 09/11] perf: Default PMU ops

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Message-ID: <1277829250.1868.46.camel@laptop>
Date:	Tue, 29 Jun 2010 18:34:10 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	Frederic Weisbecker <fweisbec@...il.com>
Cc:	paulus <paulus@...ba.org>,
	stephane eranian <eranian@...glemail.com>,
	Robert Richter <robert.richter@....com>,
	Will Deacon <will.deacon@....com>,
	Paul Mundt <lethal@...ux-sh.org>,
	Cyrill Gorcunov <gorcunov@...il.com>,
	Lin Ming <ming.m.lin@...el.com>,
	Yanmin <yanmin_zhang@...ux.intel.com>,
	Deng-Cheng Zhu <dengcheng.zhu@...il.com>,
	David Miller <davem@...emloft.net>,
	linux-kernel@...r.kernel.org
Subject: Re: [RFC][PATCH 09/11] perf: Default PMU ops

On Tue, 2010-06-29 at 17:03 +0200, Frederic Weisbecker wrote:
> > You mean, if (!pmu->start_txn && pmu->pmu_enable) { /* install defaults
> > */ } ?
> 
> 
> Not really. pmu_*able and txn are there for different purposes.
> A pmu implementation may want to provide enable/disable things
> but not require any txn. Or one may just not need any of those,
> like software events.
> 
> It should simply map to a nop if nothing is provided. 

Thing is, using at least the pmu_enable/disable fallback when no txn
methods are provided can save bunch of hardware writes. So this trivial
fallback makes sense.


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