From: Kevin Hilman <kjh-lkml@hilman.org>
To: linux-kernel@vger.kernel.org
Subject: voluntary-preemption: understanding latency trace
Date: 09 Sep 2004 03:41:07 -0700 [thread overview]
Message-ID: <83656nk9mk.fsf@www2.muking.org> (raw)
I'm seeing a mismatch between my manually-measured timings and the
timings I see in /proc/latency_trace.
I've got a SCHED_FIFO kernel thread at the highest priority
(MAX_USER_RT_PRIO-1) and it's sleeping on a wait queue. The wake is
called from an ISR. Since this thread is the highest priority in the
system, I expect it to run before the ISR threads and softIRQ threads
etc.
In the ISR I sample sched_clock() just before the call to wake_up()
and in the thread I sample sched_clock() again just after the call to
sleep. I'm seeing an almost 4ms latency between the call to wake_up
and the actual wakeup. However, in /proc/latency_trace, the worst
latency I see during the running of this test is <500us.
I must be misunderstanding how the latency traces are
started/stopped. Can anyone shed some light? Thanks.
My current setup is using -R5, running on a PII 400MHz system.
Kevin
http://hilman.org/
next reply other threads:[~2004-09-09 10:41 UTC|newest]
Thread overview: 6+ messages / expand[flat|nested] mbox.gz Atom feed top
2004-09-09 10:41 Kevin Hilman [this message]
2004-09-09 21:02 ` voluntary-preemption: understanding latency trace Lee Revell
2004-09-10 6:37 ` Ingo Molnar
2004-09-10 7:09 ` Lee Revell
2004-09-10 7:51 ` Ingo Molnar
2004-09-10 14:56 ` Kevin Hilman
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