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

[Adrian Hunter]

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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