Messages in this thread | | | Date | Thu, 26 Jan 2012 11:13:42 -0800 | From | Arun Sharma <> | Subject | Re: [PATCH] trace: reset sleep/block start time on task switch |
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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
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