linux-kernel - Re: [PATCH 1/3] Added runqueue clock normalized with cpufreq

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Date:	Fri, 17 Dec 2010 16:54:04 +0100
From:	Harald Gustafsson <hgu1972@...il.com>
To:	Thomas Gleixner <tglx@...utronix.de>
Cc:	Peter Zijlstra <peterz@...radead.org>,
	Harald Gustafsson <harald.gustafsson@...csson.com>,
	Dario Faggioli <faggioli@...dalf.sssup.it>,
	linux-kernel@...r.kernel.org, Ingo Molnar <mingo@...e.hu>,
	Claudio Scordino <claudio@...dence.eu.com>,
	Michael Trimarchi <trimarchi@...is.sssup.it>,
	Fabio Checconi <fabio@...dalf.sssup.it>,
	Tommaso Cucinotta <cucinotta@...up.it>,
	Juri Lelli <juri.lelli@...il.com>,
	Dario Faggioli <raistlin@...ux.it>
Subject: Re: [PATCH 1/3] Added runqueue clock normalized with cpufreq

2010/12/17 Thomas Gleixner <tglx@...utronix.de>:
> Also if you want to have your deadline scheduler aware of cpu
> frequency changes, then simply limit the total bandwith based on the
> lowest possible frequency and it works always. This whole dynamic
> bandwith expansion is more an academic exercise than a practical
> necessity.

This would severely limit the bandwidth available to deadline tasks. Which
then also reduces the use cases that could benefit from using sched deadline.
Also it would imply a over-reservation of the system, e.g. if you need 10%
BW of the total system and the lowest speed is at 20%, you basically need to
set a BW of 50%, to always be guaranteed that you get your 10% when cpufreq
clocks down. If you use cpufreq and want to use sched deadline this has
strong practical implications and is definitely not academic only.
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