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SubjectRe: [RFC][PATCH 09/11] perf: Default PMU ops
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On Tue, 2010-06-29 at 16:58 +0200, Frederic Weisbecker wrote:
> On Thu, Jun 24, 2010 at 04:28:13PM +0200, Peter Zijlstra wrote:
> > Provide default implementations for the pmu txn methods, this allows
> > us to remove some conditional code.
> >
> > Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
> > ---
> > kernel/perf_event.c | 48 ++++++++++++++++++++++++++++++++++++------------
> > 1 file changed, 36 insertions(+), 12 deletions(-)
> >
> > Index: linux-2.6/kernel/perf_event.c
> > ===================================================================
> > --- linux-2.6.orig/kernel/perf_event.c
> > +++ linux-2.6/kernel/perf_event.c
> > @@ -656,21 +656,14 @@ group_sched_in(struct perf_event *group_
> > {
> > struct perf_event *event, *partial_group = NULL;
> > struct pmu *pmu = group_event->pmu;
> > - bool txn = false;
> >
> > if (group_event->state == PERF_EVENT_STATE_OFF)
> > return 0;
> >
> > - /* Check if group transaction availabe */
> > - if (pmu->start_txn)
> > - txn = true;
> > -
> > - if (txn)
> > - pmu->start_txn(pmu);
> > + pmu->start_txn(pmu);
> >
> > if (event_sched_in(group_event, cpuctx, ctx)) {
> > - if (txn)
> > - pmu->cancel_txn(pmu);
> > + pmu->cancel_txn(pmu);
> > return -EAGAIN;
> > }
> >
> > @@ -684,7 +677,7 @@ group_sched_in(struct perf_event *group_
> > }
> > }
> >
> > - if (!txn || !pmu->commit_txn(pmu))
> > + if (!pmu->commit_txn(pmu))
> > return 0;
> >
> > group_error:
> > @@ -699,8 +692,7 @@ group_error:
> > }
> > event_sched_out(group_event, cpuctx, ctx);
> >
> > - if (txn)
> > - pmu->cancel_txn(pmu);
> > + pmu->cancel_txn(pmu);
> >
> > return -EAGAIN;
> > }
> > @@ -4755,6 +4747,26 @@ static struct list_head pmus;
> > static DEFINE_MUTEX(pmus_lock);
> > static struct srcu_struct pmus_srcu;
> >
> > +static void perf_pmu_nop(struct pmu *pmu)
> > +{
> > +}
> > +
> > +static void perf_pmu_start_txn(struct pmu *pmu)
> > +{
> > + perf_pmu_disable(pmu);
> > +}
> > +
> > +static int perf_pmu_commit_txn(struct pmu *pmu)
> > +{
> > + perf_pmu_enable(pmu);
> > + return 0;
> > +}
> > +
> > +static void perf_pmu_cancel_txn(struct pmu *pmu)
> > +{
> > + perf_pmu_enable(pmu);
> > +}
>
>
> So why do you need perf_pmu_*able wrappers now that you brings stubs
> if none is provided?
>
> Actually, one problem is that it makes calling two indirect nops
> for software events.
>
> Should the txn things really map to the enable/disable ops is the
> off-case? Probably better let pmu implementations deal with that.
> If they didn't provide txn implementations, it means they don't need it,
> hence it should directly map to a nop.
>

You mean, if (!pmu->start_txn && pmu->pmu_enable) { /* install defaults
*/ } ?

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