linux-kernel - Re: Scheduling the highest priority task

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Message-ID: <20070802150350.GA3030@elte.hu>
Date:	Thu, 2 Aug 2007 17:03:50 +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 01:40 PM, Ingo Molnar wrote:
> >in the SMP migration code, the 'old scheduler' indeed picks the lowest 
> >priority one, _except_ if that task is running on another CPU or is too 
> >'cache hot':
> 
> But why is it, that the scheduler picks the lowest priority one? I 
> thought sched_find_first_bit() picks the index of the lowest order bit 
> in the bitmap and thus the highest priority job. Is that wrong? What 
> needs to be changed to let the scheduler pick the highest priority 
> task from a given runqueue? I am very confused ...

it first picks the lowest index (i.e. the highest priority active 
priority-queue), but within those tasks (each task in that priority 
queue has equal priority) the load-balancer has freedom to pick any. 
Based on performance data we went for picking from the tail of the 
queue.

	Ingo
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