linux-kernel - Re: [PATCH v3 5/8] perf: Split perf_event_read

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Date:	Thu, 16 Jul 2015 14:41:24 -0700
From:	Sukadev Bhattiprolu <sukadev@...ux.vnet.ibm.com>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	Ingo Molnar <mingo@...hat.com>,
	Arnaldo Carvalho de Melo <acme@...nel.org>,
	Michael Ellerman <mpe@...erman.id.au>,
	linux-kernel@...r.kernel.org, linuxppc-dev@...ts.ozlabs.org,
	linux-s390@...r.kernel.org, sparclinux@...r.kernel.org
Subject: Re: [PATCH v3 5/8] perf: Split perf_event_read_value()

Peter Zijlstra [peterz@...radead.org] wrote:
| On Tue, Jul 14, 2015 at 08:01:52PM -0700, Sukadev Bhattiprolu wrote:
| > Move the part of perf_event_read_value() that computes the event
| > counts and event times into a new function, perf_event_compute().
| > 
| > This would allow us to call perf_event_compute() independently.
| > 
| > Signed-off-by: Sukadev Bhattiprolu <sukadev@...ux.vnet.ibm.com>
| > 
| > Changelog[v3]
| > 	Rather than move perf_event_read() into callers and then
| > 	rename, just move the computations into a separate function
| > 	(redesign to address comment from Peter Zijlstra).
| > ---
| 
| Changelog[] bits go here, below the '---' where they get discarded.

Sorry. Will fix it.

| 
| >  kernel/events/core.c |   37 ++++++++++++++++++++++++-------------
| >  1 file changed, 24 insertions(+), 13 deletions(-)
| > 
| > diff --git a/kernel/events/core.c b/kernel/events/core.c
| > index 44fb89d..b1e9a42 100644
| > --- a/kernel/events/core.c
| > +++ b/kernel/events/core.c
| > @@ -3704,6 +3704,29 @@ static int perf_release(struct inode *inode, struct file *file)
| >  	return 0;
| >  }
| >  
| > +static u64 perf_event_compute(struct perf_event *event, u64 *enabled,
| > +			      u64 *running)
| 
| This is a horrible name, 'compute' what?

We are aggregating event counts and time for children.

Would perf_event_aggregate() or perf_event_aggregate_children()
be better?

| 
| > +{
| > +	struct perf_event *child;
| > +	u64 total;
| > +
| > +	total = perf_event_count(event);
| > +
| > +	*enabled += event->total_time_enabled +
| > +			atomic64_read(&event->child_total_time_enabled);
| > +	*running += event->total_time_running +
| > +			atomic64_read(&event->child_total_time_running);
| > +
| 
| 	lockdep_assert_held(&event->child_mutex);

OK. Thanks for the comments.

Sukadev

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