From: Peter Zijlstra on
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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From: Peter Zijlstra on
On Tue, 2010-06-29 at 20:07 +0200, Frederic Weisbecker wrote:
> 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
> > > > */ } ?

> neglected pmu implementations shouldn't impact software pmus.

With the above and not providing ->pmu_enable you get that.


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From: Frederic Weisbecker on
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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From: Peter Zijlstra on
On Tue, 2010-06-29 at 20:11 +0200, Frederic Weisbecker wrote:
> On Tue, Jun 29, 2010 at 08:09:10PM +0200, Peter Zijlstra wrote:
> > On Tue, 2010-06-29 at 20:07 +0200, Frederic Weisbecker wrote:
> > > 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
> > > > > > */ } ?
> >
> > > neglected pmu implementations shouldn't impact software pmus.
> >
> > With the above and not providing ->pmu_enable you get that.
>
>
> But we don't need to provide a pmu_enable for software events, right?

My point exactly.
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From: Frederic Weisbecker on
On Tue, Jun 29, 2010 at 08:09:10PM +0200, Peter Zijlstra wrote:
> On Tue, 2010-06-29 at 20:07 +0200, Frederic Weisbecker wrote:
> > 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
> > > > > */ } ?
>
> > neglected pmu implementations shouldn't impact software pmus.
>
> With the above and not providing ->pmu_enable you get that.


But we don't need to provide a pmu_enable for software events, right?

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