linux-kernel - Re: [PATCH 05/16] sched: SCHED_DEADLINE policy implementation.

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Message-ID: <1335229437.28106.131.camel@gandalf.stny.rr.com>
Date:	Mon, 23 Apr 2012 21:03:57 -0400
From:	Steven Rostedt <rostedt@...dmis.org>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	Tommaso Cucinotta <tommaso.cucinotta@...up.it>,
	Juri Lelli <juri.lelli@...il.com>, tglx@...utronix.de,
	mingo@...hat.com, cfriesen@...tel.com, oleg@...hat.com,
	fweisbec@...il.com, darren@...art.com, johan.eker@...csson.com,
	p.faure@...tech.ch, linux-kernel@...r.kernel.org,
	claudio@...dence.eu.com, michael@...rulasolutions.com,
	fchecconi@...il.com, nicola.manica@...i.unitn.it,
	luca.abeni@...tn.it, dhaval.giani@...il.com, hgu1972@...il.com,
	paulmck@...ux.vnet.ibm.com, raistlin@...ux.it,
	insop.song@...csson.com, liming.wang@...driver.com
Subject: Re: [PATCH 05/16] sched: SCHED_DEADLINE policy implementation.

On Mon, 2012-04-23 at 23:58 +0200, Peter Zijlstra wrote:
> On Mon, 2012-04-23 at 22:55 +0100, Tommaso Cucinotta wrote:
> > why not write this straight in asm, i.e., multiply 64*64 then divide by 
> > 64 keeping the intermediate result on 128 bits? 
> 
> If you know of a way to do this for all 30 odd architectures supported
> by our beloved kernel, do let me know ;-)
> 
> Yes I can do it for x86_64, but people tend to get mighty upset if you
> break the compile for all other arches...

Use the draconian method. Make SCHED_DEADLINE dependent on
"ARCH_HAS_128_MULT" and any arch maintainer that wants SCHED_DEADLINE
for their arch will be responsible for implementing it ;-)

-- Steve


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