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Date: Fri, 17 Apr 2009 16:34:47 -0400 (EDT)
From: Christoph Lameter <cl@linux.com>
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To: Peter Zijlstra <peterz@infradead.org>
cc: Ingo Molnar <mingo@elte.hu>, linux-kernel@vger.kernel.org
Subject: Re: Scheduler regression: Too frequent timer interrupts(?)
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On Fri, 17 Apr 2009, Peter Zijlstra wrote:

> > often must occur in parallel on multiple cores. Processing is delayed if
> > any of the cores encounters a delay due to OS noise.
>
> So you have hard deadlines in the order of us? Are these SCHED_FIFO
> tasks or SCHED_OTHER?

SCHED_FIFO has the effect of removing all the involuntary context switches
but it does not effect the other interrutions.

> Your Xeon is a core2 class machine and should have relatively stable
> TSC, however its also a dual socket, which I think defeats the
> stable-ness.

> What clocksource do you have?
>
> cat /sys/devices/system/clocksource/clocksource0/current_clocksource

cat /sys/devices/system/clocksource/clocksource0/current_clocksource
tsc

> Also, looking over the rest of the scheduler tick code, I can't really
> see what would be so expensive.

The expensiveness may be fine if we can limit the number of occurences.
Maybe the histograms for those releases give more insight.