linux-kernel - Re: [RFC PATCH] perf: Add PERF_RECORD_SWITCH to indicate context switches

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Message-ID: <557B0547.4000503@intel.com>
Date:	Fri, 12 Jun 2015 19:13:59 +0300
From:	Adrian Hunter <adrian.hunter@...el.com>
To:	David Ahern <dsahern@...il.com>
CC:	Peter Zijlstra <peterz@...radead.org>,
	Andi Kleen <ak@...ux.intel.com>,
	Arnaldo Carvalho de Melo <acme@...nel.org>,
	Ingo Molnar <mingo@...nel.org>, linux-kernel@...r.kernel.org,
	Jiri Olsa <jolsa@...hat.com>,
	Stephane Eranian <eranian@...gle.com>,
	mathieu.poirier@...aro.org, Pawel Moll <pawel.moll@....com>
Subject: Re: [RFC PATCH] perf: Add PERF_RECORD_SWITCH to indicate context
 switches

On 12/06/2015 5:21 p.m., David Ahern wrote:
> On 6/12/15 4:34 AM, Adrian Hunter wrote:
>> On 12/06/15 03:47, David Ahern wrote:
>>> On 6/11/15 8:15 AM, Peter Zijlstra wrote:
>>>>> This new PERF_RECORD_SWITCH event does not have those problems
>>>>> and it also has a couple of other small advantages. It is
>>>>> easier to use because it is an auxiliary event (like mmap,
>>>>> comm and task events) which can be enabled by setting a single
>>>>> bit. It is smaller than sched:sched_switch and easier to parse.
>>>>
>>>> Right, so the one wee problem I have is that this only provides sched_in
>>>> data, I imagine people might be interested in sched_out as well.
>>>
>>> Yes and with the option of collecting callchains for sched_out.
>>
>> So what do you want that is different different from
>> PERF_COUNT_SW_CONTEXT_SWITCHES? And why?
>>
>
> My 'perf sched timehist' command can use either sched_switch and context
> switches. As you have pointed out you need to collect them system wide even if
> you only care about a subset of tasks. If you are going to add a sched_in
> there is good symmetry by also having a sched_out that is used and generated
> in a consistent manner.

Yes I will certainly add sched out, but the new thing is not a sample so it 
does not have callchains. But presumably you could use 
PERF_COUNT_SW_CONTEXT_SWITCHES as well?
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