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

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Message-ID: <20100629180745.GA11967@nowhere>
Date:	Tue, 29 Jun 2010 20:07:47 +0200
From:	Frederic Weisbecker <fweisbec@...il.com>
To:	Peter Zijlstra <peterz@...radead.org>
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, Jun 29, 2010 at 06:34:10PM +0200, Peter Zijlstra wrote:
> 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.


In this case, archs should handle that by implementing their txn.

neglected pmu implementations shouldn't impact software pmus.

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