linux-kernel - Re: [PATCH RFC 0/4] Scheduler idle notifiers and users

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Date:	Thu, 9 Feb 2012 08:51:06 +0100
From:	Ingo Molnar <mingo@...e.hu>
To:	Benjamin Herrenschmidt <benh@...nel.crashing.org>
Cc:	Dave Jones <davej@...hat.com>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Anton Vorontsov <anton.vorontsov@...aro.org>,
	Russell King <linux@....linux.org.uk>,
	Oleg Nesterov <oleg@...hat.com>,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
	Nicolas Pitre <nico@...xnic.net>, Mike Chan <mike@...roid.com>,
	Todd Poynor <toddpoynor@...gle.com>, cpufreq@...r.kernel.org,
	kernel-team@...roid.com, linaro-kernel@...ts.linaro.org,
	linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
	Arjan Van De Ven <arjan@...radead.org>
Subject: Re: [PATCH RFC 0/4] Scheduler idle notifiers and users


* Benjamin Herrenschmidt <benh@...nel.crashing.org> wrote:

> On Wed, 2012-02-08 at 15:23 -0500, Dave Jones wrote:
> > I think the biggest mistake we ever made with cpufreq was making it
> > so configurable. If we redesign it, just say no to plugin governors,
> > and
> > yes to a lot fewer sysfs knobs.
> > 
> > So, provide mechanism to kill off all the governors, and there's a
> > migration path from what we have now to something that just works
> > in a lot more cases, while remaining configurable enough for the
> > corner-cases.
> 
> On the other hand, the need for schedulable contxts may not 
> necessarily go away.

We will support it, but the *sane* hw solution is where 
frequency transitions can be done atomically. Most workloads 
change their characteristics very quickly, and so does their 
power management profile change.

The user-space driven policy model failed for that reason: it 
was *way* too slow in reacting) - and slow hardware transitions 
suck for a similar reason as well.

We accomodate all hardware as well as we can, but we *design* 
for proper hardware. So Peter is right, this should be done 
properly.

Thanks,

	Ingo
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