linux-kernel - Re: is minimum udelay() not respected in preemptible SMP kernel-2.6.23?

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Date:	Thu, 8 Nov 2007 02:20:58 +0100
From:	Andi Kleen <ak@...e.de>
To:	Matt Mackall <mpm@...enic.com>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Marin Mitov <mitov@...p.bas.bg>, linux-kernel@...r.kernel.org,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...e.hu>
Subject: Re: is minimum udelay() not respected in preemptible SMP kernel-2.6.23?


> But I think we'd be best off stashing a single bit somewhere and
> checking it at migrate time (relatively infrequent) rather than
> copying and zeroing out a potentially enormous affinity mask every
> time we disable migration (often, and in fast paths). Perhaps adding
> TASK_PINNED to the task state flags would do it?

It would need to be a count to be able to nest it.

> > get_cpu() etc. could be changed to use this then too.
>
> Some users of get_cpu might be relying on it to avoid actual
> preemption. In other words, we should have introduced a
> migrate_disable() when we first discovered the preempt/per_cpu
> conflict.

Ok perhaps it would make sense to migrate it step by step :- 
define a replacement for get_cpu and migrate over as users are getting
audited and eventually deprecate old one.

-Andi
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