linux-kernel - Re: Scheduler regression: Too frequent timer interrupts(?)

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Message-ID: <49E90F9D.5010308@nortel.com>
Date:	Fri, 17 Apr 2009 17:24:13 -0600
From:	"Chris Friesen" <cfriesen@...tel.com>
To:	Christoph Lameter <cl@...ux.com>
CC:	Peter Zijlstra <peterz@...radead.org>, Ingo Molnar <mingo@...e.hu>,
	linux-kernel@...r.kernel.org
Subject: Re: Scheduler regression: Too frequent timer interrupts(?)

Christoph Lameter wrote:

> The latencytest code simulates a busy processor (no system calls, all
> memory is prefaulted). For some reasons Linux is increasingly taking time
> away from such processes (that intentionally run uncontended on a
> dedicated processor). This causes regressions so that current upstream is
> not usable for these applications.
> 
> It would be best for these applications if the processor would be left
> undisturbed. There is likely not much that the OS needs to do on a busy
> processor if there are no competing threads and if there is no I/O taking
> place.

Peter/Ingo, could ftrace be used to determine where time is being spent 
in the kernel with suitable accuracy?   (This may be a dumb question, I 
haven't played with ftrace much.)

Given that we're talking about tens of usecs of duration, statistical 
sampling may not work all that well.

Chris
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