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

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Date:	Thu, 23 Jul 2015 09:45:09 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	Sukadev Bhattiprolu <sukadev@...ux.vnet.ibm.com>
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()

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).
> ---
>  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)
> +{
> +	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);
> +
> +	list_for_each_entry(child, &event->child_list, child_list) {
> +		perf_event_read(child);

Sure we don't want that..

> +		total += perf_event_count(child);
> +		*enabled += child->total_time_enabled;
> +		*running += child->total_time_running;
> +	}
> +
> +	return total;
> +}
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