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Date: Tue, 29 Jun 2010 20:07:47 +0200
From: Frederic Weisbecker <fweisbec@gmail.com>
To: Peter Zijlstra <peterz@infradead.org>
Cc: paulus <paulus@samba.org>, stephane eranian <eranian@googlemail.com>,
       Robert Richter <robert.richter@amd.com>,
       Will Deacon <will.deacon@arm.com>, Paul Mundt <lethal@linux-sh.org>,
       Cyrill Gorcunov <gorcunov@gmail.com>, Lin Ming <ming.m.lin@intel.com>,
       Yanmin <yanmin_zhang@linux.intel.com>,
       Deng-Cheng Zhu <dengcheng.zhu@gmail.com>,
       David Miller <davem@davemloft.net>, linux-kernel@vger.kernel.org
Subject: Re: [RFC][PATCH 09/11] perf: Default PMU ops
Message-ID: <20100629180745.GA11967@nowhere>
References: <20100624142804.431553874@chello.nl> <20100624143406.993794468@chello.nl> <20100629145806.GE5318@nowhere> <1277823591.1868.43.camel@laptop> <20100629150305.GG5318@nowhere> <1277829250.1868.46.camel@laptop>
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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.