linux-kernel - Re: [PATCH RFC 7/7] sched: energy_model: simple cpu frequency scaling policy

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Date:	Tue, 28 Oct 2014 15:27:49 +0100
From:	Peter Zijlstra <peterz@...radead.org>
To:	Mike Turquette <mturquette@...aro.org>
Cc:	mingo@...nel.org, linux-kernel@...r.kernel.org,
	preeti@...ux.vnet.ibm.com, Morten.Rasmussen@....com,
	kamalesh@...ux.vnet.ibm.com, riel@...hat.com, efault@....de,
	nicolas.pitre@...aro.org, linaro-kernel@...ts.linaro.org,
	daniel.lezcano@...aro.org, dietmar.eggemann@....com,
	pjt@...gle.com, bsegall@...gle.com, vincent.guittot@...aro.org,
	patches@...aro.org, tuukka.tikkanen@...aro.org,
	amit.kucheria@...aro.org
Subject: Re: [PATCH RFC 7/7] sched: energy_model: simple cpu frequency
 scaling policy

On Tue, Oct 21, 2014 at 11:07:31PM -0700, Mike Turquette wrote:
> Unlike legacy CPUfreq governors, this policy does not implement its own
> logic loop (such as a workqueue triggered by a timer), but instead uses
> an event-driven design. Frequency is evaluated by entering
> {en,de}queue_task_fair and then a kthread is woken from
> run_rebalance_domains which scales cpu frequency based on the latest
> evaluation.

Also note that we probably want to extend the governor to include the
other sched classes, deadline for example is a good candidate to include
as it already explicitly provides utilization requirements from which
you can compute a hard minimum frequency, below which the task set is
unschedulable.

fifo/rr are far harder to do, since for them we don't have anything
useful, the best we can do I suppose is some statistical over
provisioning but no guarantees.


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