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 11:26:03 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Alexey Budankov <alexey.budankov@...ux.intel.com>
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 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.

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