From: Arun Sharma <asharma@fb.com>
To: Peter Zijlstra <peterz@infradead.org>
Cc: Ingo Molnar <mingo@elte.hu>,
avagin@gmail.com, linux-perf-users@vger.kernel.org,
acme@ghostprotocols.net, Stephane Eranian <eranian@google.com>,
Frederic Weisbecker <fweisbec@gmail.com>
Subject: Re: Profiling sleep times?
Date: Mon, 17 Oct 2011 18:07:00 -0700 [thread overview]
Message-ID: <4E9CD134.60106@fb.com> (raw)
In-Reply-To: <1318706959.11898.1.camel@laptop>
On 10/15/11 12:29 PM, Peter Zijlstra wrote:
> On Sat, 2011-10-15 at 21:22 +0200, Peter Zijlstra wrote:
>
>>> Sleep time should really just be a different notion of 'cost of the
>>> function/callchain' and fit into the existing scheme, right?
>>
>> The problem with andrew's patches is that it wrecks the callchain
>> semantics. The waittime tracepoint is in the wakeup path (and hence
>> generates the wakee's callchain) whereas they really want the callchain
>> of the woken task to show where it spend time.
>
> We could of course try to move the tracepoint into the schedule path, so
> we issue it the first time the task gets scheduled after the wakeup, but
> I suspect that will just add more overhead, and we really could do
> without that.
Do we need to define new tracepoints? I suspect we could make the
existing ones:
trace_sched_stat_wait()
trace_sched_stat_sleep()
work for this purpose. The length of time the task was not on the cpu
could then be computed as: sleep+wait. The downside is that the
complexity moves to user space.
perf record -e sched:sched_stat_sleep,sched:sched_stat_wait,...
Re: changing the semantics of tracepoint callchains
Yeah - this could be surprising. Luckily, most tracepoints retain their
semantics, but a few special ones don't. I guess we just need to
document the new behavior.
-Arun
next prev parent reply other threads:[~2011-10-18 1:07 UTC|newest]
Thread overview: 23+ messages / expand[flat|nested] mbox.gz Atom feed top
2011-10-03 19:38 Profiling sleep times? Arun Sharma
2011-10-03 20:17 ` Peter Zijlstra
2011-10-03 21:53 ` Arun Sharma
2011-10-04 8:34 ` Peter Zijlstra
2011-10-06 21:56 ` Arun Sharma
2011-10-07 0:05 ` Arun Sharma
2011-10-07 1:30 ` Peter Zijlstra
2011-10-07 5:42 ` avagin
2011-10-07 9:33 ` Peter Zijlstra
2011-10-07 17:58 ` Arun Sharma
2011-10-07 23:16 ` avagin
2011-10-08 1:45 ` avagin
2011-10-10 18:50 ` Arun Sharma
2011-10-12 7:41 ` Ingo Molnar
2011-10-13 5:39 ` Andrew Vagin
2011-10-14 21:19 ` Arun Sharma
2011-10-15 17:00 ` Ingo Molnar
2011-10-15 19:22 ` Peter Zijlstra
2011-10-15 19:29 ` Peter Zijlstra
2011-10-18 1:07 ` Arun Sharma [this message]
2011-10-22 10:49 ` Frederic Weisbecker
2011-10-22 16:22 ` Andrew Wagin
2011-10-23 0:27 ` Arun Sharma
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