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

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Message-ID: <alpine.DEB.1.10.0904171100510.21575@qirst.com>
Date:	Fri, 17 Apr 2009 11:04:41 -0400 (EDT)
From:	Christoph Lameter <cl@...ux.com>
To:	Peter Zijlstra <peterz@...radead.org>
cc:	Ingo Molnar <mingo@...e.hu>, linux-kernel@...r.kernel.org
Subject: Re: Scheduler regression: Too frequent timer interrupts(?)

On Fri, 17 Apr 2009, Peter Zijlstra wrote:

> And a random 1us cutoff, is well, random.

Its got to be somewhere.

> If you want to reduce interrupts, that's fine, but not counting an
> interrupt because its below the magic 1us marker sounds a bit, well,
> magic -- might work for you, might not for me on another machine, might
> even be compiler dependent.

The point is to reduce the interrupts of user space application. Hardware
interrupts etc are something else. Maybe I should not use the term
interrupt. Cpu unavailability? Cache pollution?

> So 5 <1us interruption are not at all accounted, whereas a single 1>us
> interruption is. I'd rather get rid of those 5 than try and shave a bit
> of the one, if you get what I mean.

Ok. We can set the threshold lower and see how that goes.

> Furthermore, yes the scheduler is one of those jiffy tick users, but
> there are more. We can do ntp/gtod things in there, there is process
> accounting, there is some RCU machinery, timers etc..

Again things were fine before the scheduler changed.

Could we defer interrupts if a single process is running on a cpu and
there is no other process on the runqueue and no other use of the timer
interrupt?

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