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

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Message-ID: <20180416135957.GC23802@kernel.org>
Date:   Mon, 16 Apr 2018 10:59:57 -0300
From:   Arnaldo Carvalho de Melo <acme@...nel.org>
To:     Alexey Budankov <alexey.budankov@...ux.intel.com>
Cc:     Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...hat.com>,
        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

Em Mon, Apr 16, 2018 at 11:29:03AM +0300, Alexey Budankov escreveu:
> Hi Arnaldo,
> 
> 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.
> 
> This is just to make sure it doesn't sneak out of your attention 
> in hope the plan is still the same as Peter mentioned above.

Will look into this now.
 
> Thanks,
> Alexey
> 
> > 
> >> 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);
> >