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Subject: Re: [RFC][PATCH 09/11] perf: Default PMU ops
From: Peter Zijlstra <peterz@infradead.org>
To: Frederic Weisbecker <fweisbec@gmail.com>
Cc: paulus <paulus@samba.org>, stephane eranian <eranian@googlemail.com>,
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Date: Tue, 29 Jun 2010 18:34:10 +0200
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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.