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

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Message-ID: <1329322147.2293.145.camel@twins>
Date:	Wed, 15 Feb 2012 17:09:07 +0100
From:	Peter Zijlstra <a.p.zijlstra@...llo.nl>
To:	Russell King - ARM Linux <linux@....linux.org.uk>
Cc:	Saravana Kannan <skannan@...eaurora.org>,
	Ingo Molnar <mingo@...e.hu>, linaro-kernel@...ts.linaro.org,
	Nicolas Pitre <nico@...xnic.net>,
	Benjamin Herrenschmidt <benh@...nel.crashing.org>,
	Oleg Nesterov <oleg@...hat.com>, cpufreq@...r.kernel.org,
	linux-kernel@...r.kernel.org,
	Anton Vorontsov <anton.vorontsov@...aro.org>,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
	Mike Chan <mike@...roid.com>, Dave Jones <davej@...hat.com>,
	Todd Poynor <toddpoynor@...gle.com>, kernel-team@...roid.com,
	linux-arm-kernel@...ts.infradead.org,
	Arjan Van De Ven <arjan@...radead.org>,
	Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [PATCH RFC 0/4] Scheduler idle notifiers and users

On Wed, 2012-02-15 at 16:00 +0000, Russell King - ARM Linux wrote:
> 
> > A third possibility is to self-IPI and take it from there.. assuming
> > these platforms can actually self-IPI.
> 
> Even if there was an IPI (not talking about SMP anyway) I'm not sure
> what good it would be.  We can (and do) get an IRQ from the LCD
> controller when its shutdown is complete, but that would have to be
> somehow propagated back up to the cpufreq code.  And the cpufreq code
> would have to know that the LCD controller was alive and therefore had
> to be waited for.  All sounds rather yucky to me. 

If can self-ipi from the scheduler context (which has IRQs disabled),
once you get to the ipi handler your scheduler locks are gone and you
can queue a worklet or wake some kthread to do all the sleeping stuff.


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