linux-kernel - Re: RFC: THE OFFLINE SCHEDULER

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Message-ID: <20090826210812.GA22765@elte.hu>
Date:	Wed, 26 Aug 2009 23:08:12 +0200
From:	Ingo Molnar <mingo@...e.hu>
To:	Christoph Lameter <cl@...ux-foundation.org>
Cc:	Peter Zijlstra <peterz@...radead.org>,
	raz ben yehuda <raziebe@...il.com>,
	Maxim Levitsky <maximlevitsky@...il.com>,
	Chris Friesen <cfriesen@...tel.com>,
	Mike Galbraith <efault@....de>, riel@...hat.com,
	andrew motron <akpm@...ux-foundation.org>,
	wiseman@...s.biu.ac.il, lkml <linux-kernel@...r.kernel.org>,
	linux-rt-users@...r.kernel.org
Subject: Re: RFC: THE OFFLINE SCHEDULER


* Christoph Lameter <cl@...ux-foundation.org> wrote:

> > to have sharp teeth nor any apparent poison fangs) - i simply 
> > concur with the reasons Peter listed that it is a technically 
> > inferior solution.
> 
> Ok so you are saying that the reduction of OS latencies will make 
> the processor completely available and have no disturbances like 
> OFFLINE scheduling?

I'm saying that your lack of trying to reduce even low-hanging-fruit 
latency sources that were pointed out to you fundamentally destroys 
your credibility in claiming that they are unfixable for all 
practical purposes.

Or, to come up with a car analogy: it's a bit as if at a repair shop 
you complained that your car has a scratch on its cooler grid that 
annoys you, and you insisted that it be outfitted with a new diesel 
engine which needs no cooler grid (throwing away the nice Hemi block 
it has currently) - and ignored the mechanic's opinion that he loves 
the Hemi and that to him the scratch looks very much like bird-sh*t 
and that a proper car wash might do the trick too ;-)

> Peter has not given a solution to the problem. Nor have you.

What do you mean by 'has given a solution' - a patch?

Peter mentioned a few things that you can try to reduce the 
worst-case latency of the timer tick.

Peter also implemented the hr-tick solution (CONFIG_SCHED_HRTICK) - 
it's mostly upstream but disabled because it had problems - if you 
are interested in improving this area you can fix and complete it.

That would benefit ordinary Linux users too, not just rare isolation 
apps.

	Ingo
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