linux-kernel - Re: [PATCH v5 1/3] perf/core: store context switch out type into Perf trace

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Date:   Mon, 9 Apr 2018 12:56:00 +0300
From:   Alexey Budankov <alexey.budankov@...ux.intel.com>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     Ingo Molnar <mingo@...hat.com>,
        Arnaldo Carvalho de Melo <acme@...nel.org>,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        Jiri Olsa <jolsa@...hat.com>,
        Namhyung Kim <namhyung@...nel.org>,
        Andi Kleen <ak@...ux.intel.com>,
        linux-kernel <linux-kernel@...r.kernel.org>,
        linux-perf-users@...r.kernel.org
Subject: Re: [PATCH v5 1/3] perf/core: store context switch out type into Perf
 trace

On 09.04.2018 12:26, Peter Zijlstra wrote:
> On Mon, Apr 09, 2018 at 10:25:32AM +0300, Alexey Budankov wrote:
>>
>> Store preempting context switch out event into Perf trace as a part of 
>> PERF_RECORD_SWITCH[_CPU_WIDE] record.
>>
>> Percentage of preempting and non-preempting context switches help 
>> understanding the nature of workloads (CPU or IO bound) that are running 
>> on a machine;
>>
>> The event is treated as preemption one when task->state value of the 
>> thread being switched out is TASK_RUNNING. Event type encoding is 
>> implemented using PERF_RECORD_MISC_SWITCH_OUT_PREEMPT bit;
>> 	
>> Signed-off-by: Alexey Budankov <alexey.budankov@...ux.intel.com>
> 
> Acked-by: Peter Zijlstra (Intel) <peterz@...radead.org>
> 
> Acme, I'm thinking you should route this, since most of the changes are
> actually to the tool.
> 
>> diff --git a/kernel/events/core.c b/kernel/events/core.c
>> index fc1c330c6bd6..872a5aaa77eb 100644
>> --- a/kernel/events/core.c
>> +++ b/kernel/events/core.c
>> @@ -7584,6 +7584,10 @@ static void perf_event_switch(struct task_struct *task,
>>  		},
>>  	};
>>  
>> +	if (!sched_in && task->state == TASK_RUNNING)
>> +		switch_event.event_id.header.misc |=
>> +				PERF_RECORD_MISC_SWITCH_OUT_PREEMPT;
> 
> I typically prefer {} over any multi-line expression.

Yep, makes sense. Sorry for missing that here.

> 
>>  	perf_iterate_sb(perf_event_switch_output,
>>  		       &switch_event,
>>  		       NULL);
>