linux-kernel - Re: [PATCH v2 1/6] perf: Add interface to add general events to sysfs

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Date:	Tue, 19 Jul 2011 15:52:06 +0800
From:	Lin Ming <ming.m.lin@...el.com>
To:	Peter Zijlstra <a.p.zijlstra@...llo.nl>
Cc:	Ingo Molnar <mingo@...e.hu>, Andi Kleen <andi@...stfloor.org>,
	Stephane Eranian <eranian@...gle.com>,
	Arnaldo Carvalho de Melo <acme@...stprotocols.net>,
	linux-kernel <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2 1/6] perf: Add interface to add general events to
 sysfs

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
> > └── cycle
> > 
> > Signed-off-by: Lin Ming <ming.m.lin@...el.com>
> > ---
> >  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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