[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]
Message-ID: <4F21A5E6.9030305@fb.com>
Date: Thu, 26 Jan 2012 11:13:42 -0800
From: Arun Sharma <asharma@...com>
To: Frederic Weisbecker <fweisbec@...il.com>
CC: Steven Rostedt <rostedt@...dmis.org>,
Peter Zijlstra <a.p.zijlstra@...llo.nl>,
<linux-kernel@...r.kernel.org>,
Arnaldo Carvalho de Melo <acme@...radead.org>,
Andrew Vagin <avagin@...nvz.org>, Ingo Molnar <mingo@...e.hu>
Subject: Re: [PATCH] trace: reset sleep/block start time on task switch
On 1/25/12 6:27 PM, Frederic Weisbecker wrote:
>> Even if we resolve the sampling rate related problems, there is the
>> issue of: can we trust that a sampled sched_switch event and a
>> sampled sched_stat_sleep event actually match each other?
>
> Well, a sched_stat_sleep event should match the sched_switch with
> prev as the last targeted task.
>
> Or am I missing something?
I was thinking about large systems with 100k+ sched_switch events, where
the user wants to just sample 1k events/sec.
perf record -F 1000 -e sched:sched_switch -a -- sleep 1
Doesn't look like we're using sampling for tracepoint events? The rest
of this makes sense only if we're sampling tracepoint events (eg: to
limit the impact on the system being profiled/traced).
On a system with 50k sched_switch and 10k sched_stat_sleep events, if we
sample at 1000 events/sec, we may lose an event of interest either due
to finite buffer sizes or to sampling, which is why a single event based
sleep profiling is of interest to us.
On 1/25/12 6:21 PM, Frederic Weisbecker wrote:
>
> Have you tried to tweak the -m options to increase the size of the
buffer?
-m4:
Processed 276875 events and lost 4772 chunks!
Check IO/CPU overload!
-m5:
Fatal: failed to mmap with 22 (Invalid argument)
-Arun
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/
Powered by blists - more mailing lists