Re: [RFC PATCH] perf: Add PERF_RECORD_SWITCH to indicate context switches
From: David Ahern
Date: Fri Jun 12 2015 - 10:29:18 EST
On 6/12/15 5:12 AM, Adrian Hunter 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.
That is not a problem although it would be interesting to know the use-case.
To me it seemed unreasonable to expect to analyze scheduler behaviour
without admin-level privileges since it is inherently an administrative
activity.
One use case is wanting to analyze a set of processes -- how long they
run when scheduled, where they are when scheduled out, scheduling delay
on wakeups, time between scehd in. I wrote the timehist tool in 2010 it
has been really helpful understanding what is happening on each cpu and
characteristics of a set of processes (e.g. ping ponging between tasks
sending messages to each other).
In this case it is not necessarily scheduler behavior (though it does it
enter the picture to a degree), but rather behavior of a process or set
of tasks.
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