linux-kernel - Re: [PATCH v2 0/3] perf/core: expose thread context switch out event type to user space

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Message-ID: <c727a309-6fe5-22ac-0072-30724127166b@linux.intel.com>
Date:   Fri, 23 Mar 2018 23:38:03 +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>,
        linux-kernel <linux-kernel@...r.kernel.org>,
        Andi Kleen <ak@...ux.intel.com>
Subject: Re: [PATCH v2 0/3] perf/core: expose thread context switch out event
 type to user space

On 23.03.2018 21:05, Peter Zijlstra wrote:
> On Thu, Mar 22, 2018 at 07:08:25PM +0300, Alexey Budankov wrote:
>>
>> Implementation of exposing context-switch-out type event as a part 
>> of PERF_RECORD_SWITCH[_CPU_WIDE] record.
>>
>> Introduced types of events assumed to be:
>> a) preempt: when task->state == TASK_RUNNING
>> b) yield: !preempt, encoding is done using new bit 
>>    PERF_RECORD_MISC_SWITCH_OUT_YIELD like this:
> 
> A !preempt context switch isn't nessecarily a yield; please don't use
> that name, it means something quite specific and this isn't it.
> 
> Specifically, on Linux yield() doesn't actually change task->state, so
> when task->state is set !0 it _cannot_ have been yield.
> 
> I would invert the thing and call the preempt one SWITCH_OUT_PREEMPT.
> 

Make sense. This way it names the thing exactly what it is. 
Let me take care of that.

Thanks,
Alexey