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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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