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

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Message-ID: <20120211144530.GA497@elte.hu>
Date:	Sat, 11 Feb 2012 15:45:30 +0100
From:	Ingo Molnar <mingo@...e.hu>
To:	Saravana Kannan <skannan@...eaurora.org>
Cc:	Benjamin Herrenschmidt <benh@...nel.crashing.org>,
	Todd Poynor <toddpoynor@...gle.com>,
	Russell King <linux@....linux.org.uk>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Nicolas Pitre <nico@...xnic.net>,
	Oleg Nesterov <oleg@...hat.com>, cpufreq@...r.kernel.org,
	linux-kernel@...r.kernel.org,
	Anton Vorontsov <anton.vorontsov@...aro.org>,
	linaro-kernel@...ts.linaro.org, Mike Chan <mike@...roid.com>,
	Dave Jones <davej@...hat.com>,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
	kernel-team@...roid.com, linux-arm-kernel@...ts.infradead.org,
	Arjan Van De Ven <arjan@...radead.org>
Subject: Re: [PATCH RFC 0/4] Scheduler idle notifiers and users


* Saravana Kannan <skannan@...eaurora.org> wrote:

> When you say accommodate all hardware, does it mean we will 
> keep around CPUfreq and allow attempts at improving it? Or we 
> will completely move to scheduler based CPU freq scaling, but 
> won't try to force atomicity? Say, may be queue up a 
> notification to a CPU driver to scale up the frequency as soon 
> as it can?

I don't think we should (or even could) force atomicity - we 
adapt to whatever the hardware can do.

But the design should be directed at systems where frequency 
changes can be done in a reasonably fast manner. That is what he 
future is - any change we initiate today takes years to reach 
actual products/systems.

> IMHO, I think the problem with CPUfreq and its dynamic 
> governors today is that they do a timer based sampling of the 
> CPU load instead of getting some hints from the scheduler when 
> the scheduler knows that the load average is quite high.

Yes - that is one of the "frequency changes are slow" 
assumptions - which is wrong.

Thanks,

	Ingo
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