linux-kernel - Re: 2.6.19 -mm merge plans

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Date:	Fri, 22 Sep 2006 16:12:46 -0400
From:	Dave Jones <davej@...hat.com>
To:	Pavel Machek <pavel@...e.cz>
Cc:	Ingo Molnar <mingo@...e.hu>, Andrew Morton <akpm@...l.org>,
	linux-kernel@...r.kernel.org, Thomas Gleixner <tglx@...utronix.de>,
	John Stultz <johnstul@...ibm.com>,
	Arjan van de Ven <arjan@...radead.org>
Subject: Re: 2.6.19 -mm merge plans

On Fri, Sep 22, 2006 at 01:06:48PM +0000, Pavel Machek wrote:

 > > would be nice to merge the -hrt queue that goes right ontop this queue. 
 > > Even if HIGH_RES_TIMERS is "default n" in the beginning. That gives us 
 > > high-res timers and dynticks which are both very important features to 
 > > certain classes of users/devices.
 > 
 > dynticks give benefit of 0.3W, or 20minutes (IIRC) from 8hours on thinkpad
 > x60... and they were around for way too long. (When baseline is
 > hz=250, it is 0.5W from hz=1000 baseline). It would be cool to
 > finally merge them.

I actually saw much bigger wins when I tested with an Athlon XP based compaq laptop
a year or so back. dynticks moved idle from being stuck at 21W to a sinusoidal
cycle in single watt increments between 22W->18W.  It would never stay in the
lower ranges for long because of timers firing all the time.

See http://kernelslacker.livejournal.com/33637.html for details.

There is much interest right now in fixing up various bits of userspace
to not do braindead things with timers/polling.  The gnome people
have recently come up with a timertop-esque hack (that goes a bit further)
for eg. See http://blogs.gnome.org/ryanl for details.
Arjan also recently did battle with a huge amount of really dumb userspace,
and dwmw2 has been tracking a bunch of these for OLPC:
https://bugzilla.redhat.com/bugzilla/showdependencytree.cgi?id=204948

Damn all these busy people making me feel inadequate :)

	Dave
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