linux-kernel - Re: [PATCH 13/13] RT: Cache cpus_allowed weight for optimizing migration

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Date:	Wed, 24 Oct 2007 02:19:23 +0200
From:	Ingo Oeser <ioe-lkml@...eria.de>
To:	Gregory Haskins <ghaskins@...ell.com>
Cc:	linux-rt-users@...r.kernel.org, linux-kernel@...r.kernel.org,
	Steven Rostedt <rostedt@...dmis.org>,
	Dmitry Adamushko <dmitry.adamushko@...il.com>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Ingo Molnar <mingo@...e.hu>, Darren Hart <dvhltc@...ibm.com>
Subject: Re: [PATCH 13/13] RT: Cache cpus_allowed weight for optimizing migration

Hi Gregory,

On Tuesday 23 October 2007, Gregory Haskins wrote:
> Calculating the weight is probably relatively expensive, so it is only
> done when the cpus_allowed mask is updated (which should be relatively
> infrequent, especially compared to scheduling frequency) and cached in
> the task_struct.

Why not make it a task flag, since according to your code, you are only 
interested whether this is <= 1 or > 1. Since !(x <= 1) <=> (x > 1)
for any given unsigned integer x, the required data structure is
a "boolean" or a flag.


Best Regards

Ingo Oeser
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