Re: [PATCH v2 1/6] perf: Add interface to add general events tosysfs

From: Lin Ming
Date: Tue Jul 19 2011 - 03:52:13 EST


On Mon, 2011-07-18 at 21:34 +0800, Peter Zijlstra wrote:
> On Fri, 2011-07-15 at 14:34 +0000, Lin Ming wrote:
> > PMU can implement ::add_events() to add its general events to sysfs.
> >
> > For example,
> >
> > /sys/bus/event_source/devices/uncore/events
> > âââ cycle
> >
> > Signed-off-by: Lin Ming <ming.m.lin@xxxxxxxxx>
> > ---
> > include/linux/perf_event.h | 9 +++++++
> > kernel/events/core.c | 52 ++++++++++++++++++++++++++++++++++++++++++++
> > 2 files changed, 61 insertions(+), 0 deletions(-)
> >
> > diff --git a/include/linux/perf_event.h b/include/linux/perf_event.h
> > index 3f2711c..14337a3 100644
> > --- a/include/linux/perf_event.h
> > +++ b/include/linux/perf_event.h
> > @@ -676,6 +676,14 @@ struct pmu {
> > * for each successful ->add() during the transaction.
> > */
> > void (*cancel_txn) (struct pmu *pmu); /* optional */
> > +
> > + void (*add_events) (void);
> > +};
>
> I'd rather not have a function pointer here, and all the kobj thingies
> can be hooking into the existing struct device, right?

I forgot to mention one important reason why I added a function pointer.

The events can only be added to sysfs after PMU sysfs is initialized in
perf_event_sysfs_init ->
pmu_dev_alloc

> @@ -5571,6 +5571,8 @@ static int pmu_dev_alloc(struct pmu *pmu)
> if (ret)
> goto free_dev;
>
> + if (pmu->add_events)
> + pmu->add_events();

So we need a pmu callback which is called in pmu_dev_alloc to add events
to sysfs.

You suggested a new interface,
int perf_pmu_add_event(struct pmu *pmu, const char *name, u64 config)

But where should it be called?
I guess you mean to call it in pmu init function, for example,
uncore_pmu_init.

But pmu init function maybe called before perf_event_sysfs_init, which
means the pmu sysfs has not been initialized yet.

Lin Ming

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