Re: [PATCH] sched: split sched_switch trace event into two

[Peter Zijlstra <peterz@infradead.org>]

On Wed, Jun 24, 2015 at 04:19:33PM -0700, Cong Wang wrote:
> Currently we only have one sched_switch trace event
> for task switching, which is generated very early during
> task switch. When we try to monitor per-container events,
> this is not what we expect.

Adjust your expectations?

> For example, we have a process A which is in the cgroup
> we monitor, and process B which isn't, when kernel switches
> from B to A, the sched_switch event is not recorded for this
> cgroup since it belongs to B (current process is still B
> util we finish the switch), but we require this event to
> signal that process A in this cgroup gets scheduled. This is
> crucial for calculating schedule latency.

I don't get it. This is global data in the root pid-space.

The switch data includes both the previous and the next task. Just look
up their corresponding cgroups and be done with it.

If you cannot get what you want from it, you're doing it wrong.