linux-kernel - Re: [PATCH v4 06/22] perf: Redirect output from inherited events to parents

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Date:	Mon, 8 Sep 2014 17:26:55 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	Alexander Shishkin <alexander.shishkin@...ux.intel.com>
Cc:	Ingo Molnar <mingo@...hat.com>, linux-kernel@...r.kernel.org,
	Robert Richter <rric@...nel.org>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Mike Galbraith <efault@....de>,
	Paul Mackerras <paulus@...ba.org>,
	Stephane Eranian <eranian@...gle.com>,
	Andi Kleen <ak@...ux.intel.com>, kan.liang@...el.com
Subject: Re: [PATCH v4 06/22] perf: Redirect output from inherited events to
 parents

On Wed, Aug 20, 2014 at 03:36:03PM +0300, Alexander Shishkin wrote:
> In order to collect AUX data from an inherited event, we can redirect its
> output to parent's ring buffer if possible (they must be cpu affine). This
> patch adds set_output() to the inheritance path.
> 
> Signed-off-by: Alexander Shishkin <alexander.shishkin@...ux.intel.com>
> ---
>  kernel/events/core.c | 6 ++++++
>  1 file changed, 6 insertions(+)
> 
> diff --git a/kernel/events/core.c b/kernel/events/core.c
> index 67f857ab56..e36478564c 100644
> --- a/kernel/events/core.c
> +++ b/kernel/events/core.c
> @@ -7962,6 +7962,12 @@ inherit_event(struct perf_event *parent_event,
>  		= parent_event->overflow_handler_context;
>  
>  	/*
> +	 * Direct child's output to parent's ring buffer (if any)
> +	 */
> +	if (parent_event->cpu != -1)
> +		(void)perf_event_set_output(child_event, parent_event);
> +
> +	/*
>  	 * Precalculate sample_data sizes
>  	 */
>  	perf_event__header_size(child_event);

Uhm, nope, see perf_output_begin(), it always redirects output to parent
events.

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