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

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Message-ID: <1328736834.2903.33.camel@pasglop>
Date:	Thu, 09 Feb 2012 08:33:54 +1100
From:	Benjamin Herrenschmidt <benh@...nel.crashing.org>
To:	Dave Jones <davej@...hat.com>
Cc:	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Anton Vorontsov <anton.vorontsov@...aro.org>,
	Ingo Molnar <mingo@...e.hu>,
	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

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.

If you look beyond x86, there's several issues that get into the
picture. i2c clock chips & power control chips are slow (the i2c bus
itself is). You don't want to spin for hundreds of microsecs while you
do those transactions.

I have seen many cases where the clock control can be done quite
quickly, but on the other hand, the voltage control takes dozens of ms
to reach the target value & stabilize.

That could be done asynchronously .. as long as the scheduler doesn't
constantly hammer it with change requests.

Cheers,
Ben.


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