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

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Date:	Tue, 09 Sep 2014 12:54:04 +0300
From:	Alexander Shishkin <alexander.shishkin@...ux.intel.com>
To:	Peter Zijlstra <peterz@...radead.org>
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

Peter Zijlstra <peterz@...radead.org> writes:

> 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.

Ouch, indeed. We'll just do the same in perf_aux_output_begin().

Regards,
--
Alex
--
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