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<div class="moz-cite-prefix">Le 2013-08-12 11:15, Kannan Ramaswamy a
écrit :<br>
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<blockquote cite="mid:BLU170-W489208B5DACFA89CF0F8ADB85B0@phx.gbl"
type="cite">
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<div dir="ltr">Hi,
<div>I am new to lttng and am reading through the documentation.
Does anyone have experience tracing linux scheduler latencies
with lttng? I will be grateful if you could provide a cheat
sheet of instructions to follow. I want to get a call trace of
kernel operations for each time the scheduler wakeup was over
some prespecified microsecond duration.</div>
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</blockquote>
<br>
The scheduler latency is the delay between a task becomes runnable
and the time it's actually running. The event that indicates the
task was waiting and is now runnable is sched_wakeup (or
sched_wakeup_new in the case of a newly forked task). The time
between this event and it's corresponding sched_switch indicates the
scheduling latency. <br>
<br>
I'm using Java library to do the analysis. Here is a simple example
of how to perform some analysis on a trace. <br>
<br>
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<a
href="https://github.com/giraldeau/org.eclipse.linuxtools.lttng2.kmem">https://github.com/giraldeau/org.eclipse.linuxtools.lttng2.kmem</a><br>
<br>
<blockquote cite="mid:BLU170-W489208B5DACFA89CF0F8ADB85B0@phx.gbl"
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<div><br>
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<div>I have compiled lttng 2.2 on a vanilla 3.10.5 kernel on a
16 core Intel Xeon CPU E5-2690 @2.90GHz. I am trying to
identify and reduce my multithreaded multicast based
application service latency.</div>
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</blockquote>
<br>
You should make sure there is no event loss, because it would yield
wrong results. You can increase kernel buffer size when enabling
channels. Have a look at how it's done in lttng-simple. <br>
<br>
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<a
href="https://github.com/giraldeau/workload-kit/blob/master/utils/lttng-simple">https://github.com/giraldeau/workload-kit/blob/master/utils/lttng-simple</a><br>
<br>
Is it an open source app? Is it possible to publish the traces? I
could take a look at it. <br>
<br>
Cheers,<br>
<br>
Francis<br>
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