linux-kernel - Re: hires timer patchset [was Re: 2.6.19 -mm merge plans]

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Date:	Sat, 23 Sep 2006 21:22:25 +0200
From:	Voluspa <lista1@...hem.se>
To:	Daniel Walker <dwalker@...sta.com>
Cc:	brugolsky@...emetry-investments.com, mingo@...e.hu, pavel@...e.cz,
	akpm@...l.org, tglx@...utronix.de, linux-kernel@...r.kernel.org
Subject: Re: hires timer patchset [was Re: 2.6.19 -mm merge plans]

On Sat, 23 Sep 2006 11:09:26 -0700 Daniel Walker wrote:
> On Sat, 2006-09-23 at 04:17 +0200, Voluspa wrote:
> 
> > Here's another data point: I tried 2.6.18-rt3 today on a x86_64
> > notebook. I'm on an eternal quest for extended battery time, so
> > NO_HZ would be perfect. Long story shortened, HIGH_RES_TIMERS
> > (prerequisite for NO_HZ) caused the CPU to never step down from max
> > speed (ondemand, powernow_k8) at 2200 MHz.
> > 
> > In addition, something invisible used very frequent bursts of ~30%
> > SYS CPU. Turning from PREEMPT_RT to PREEMPT_DESKTOP introduced
> > occasional bursts of ~50% USER CPU (mixed with the SYS). Toggling
> > RCU model made no difference.
> > 
> 
> It seems like you don't need all of 2.6.18-rt3 , you just want dynamic
> tick .. You can obtain just the HRT/dynamic tick patch from here,
> 
> http://www.tglx.de/projects/hrtimers/2.6.18/

Thank you pointing that out. I didn't realise that the features were so
sharply divided. Perhaps I'll even be able to debug it locally, then -
wearing ear-mufflers. I'm not kidding about the fan noise.

At the very least the experiment will tell if it's a -rt combo problem
or NO_HZ on its own.

Mvh
Mats Johannesson
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