Re: [patch] Real-Time Preemption, -RT-2.6.12-rc6-V0.7.48-00

From: Ingo Molnar
Date: Wed Jun 22 2005 - 03:47:36 EST

* William Weston <weston@xxxxxxxxx> wrote:

> Attached are two typical traces and the .config from my Xeon/HT box,
> currently running -50-06 with a normal desktop workload (X, wmaker,
> ten dockapps, several xterms, and firefox).

the second trace seems to be a cross-CPU wakeup bug. It's not completely
clear from the trace what happened - but we measured the latency of a
task (wmcube-3191), where the wakeup happened on CPU#0 and wmcube-3191
was queued to CPU#1 which was idle at that time. The bug is that it
wasnt until timestamp 306us that this actually happened - and CPU#1 was
just idling around in default_idle() for no good reason. CPU#1 should
have run wmcube-3191 at around timestamp 13us.

I've uploaded the -50-07 kernel which will put some more info into the
traces - could you try to repeat the measurement and get similar
latencies? As i guess you already found out that you can always reset
the measurement to get a new set of traces, via:

echo 0 > /proc/sys/kernel/preempt_max_latency

(it's not a problem if you send me multiple latency traces, i'll figure
out which is the most useful one.)

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