linux-kernel - Re: Scheduling the highest priority task

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Message-ID: <20070802194825.GA23245@elte.hu>
Date:	Thu, 2 Aug 2007 21:48:25 +0200
From:	Ingo Molnar <mingo@...e.hu>
To:	Martin Roehricht <ml@...icis.org>
Cc:	linux-kernel@...r.kernel.org
Subject: Re: Scheduling the highest priority task


* Martin Roehricht <ml@...icis.org> wrote:

> On 08/02/2007 05:19 PM, Ingo Molnar wrote:
> >* Martin Roehricht <ml@...icis.org> wrote:
> >
> >>That's fine with me, that within the same priority-queue any task can 
> >>be chosen. But assume two tasks with highly different priorities, such 
> >>as 105 and 135 are scheduled on the same processor and one of them is 
> >>now to be migrated -- shouldn't be the queue with task P=105 
> >>considered first for migration by this code? Both tasks would use 
> >>different queues with their own linked lists, right?
> >
> >yes. What makes you believe that the lower priority one (prio 135) is 
> >chosen? [ as i said before, that will only be chosen if all tasks in the 
> >higher-priority queue (prio 105) are either already running on a CPU or 
> >have recently run so that the cache-hot logic skips them. ]
> 
> This believe is primarily based on my observations of multiple 
> benchmark runs and also on your statement earlier: »in the SMP 
> migration code, the 'old scheduler' indeed picks the lowest priority 
> one«.

oh, sorry, that was meant to be the 'highest priority one' :-/

so i think you got it all right, i just typoed that first sentence.

	Ingo
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