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SubjectRe: [patch] Real-Time Preemption, -RT-2.6.9-mm1-V0

* Ingo Molnar <mingo@elte.hu> wrote:

> > Still problems with interactive behavior. Running KDE, with top
> > running in xterm, scrolling through the menus I get some pauses. When
> > the pauses occur I see kdeinit hit the top of the list and sometimes
> > consuming 90% or more of a CPU and idle usage drops to 30-40%. I do
> > see some latency traces (not really high ones) in the log that were
> > generated by kdeinit but I think they were generated prior to when
> > these pauses occurred, most likely when logging in.
>
> is this 90% or more CPU time system (kernel) overhead or userspace
> overhead?

another thing to watch for is the context-switch rate in vmstat. -V0.3
patches include a hack that include involuntary context-switches (mutex
context switches) in the context-switch stat as well. (previously those
were reported in a separate field which vmstat didnt pick up.)

So if the context-switch rate shots up to above say 100K/sec that is a
sure sign of some mutex badness. The livelock scenarios i solved in
-V0.3 occasionally generated a more than 500K/sec context-switch rate on
a 2GHz box. Having just a couple of thousand per sec isnt by itself a
sign of anything unusual.

Ingo
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