linux-kernel - Re: [RFC] Correct behaviour of irq affinity?

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Message-Id: <200903251103.10249.rusty@rustcorp.com.au>
Date:	Wed, 25 Mar 2009 11:03:08 +1030
From:	Rusty Russell <rusty@...tcorp.com.au>
To:	"Eric W. Biederman" <ebiederm@...ssion.com>
Cc:	x86@...nel.org, linux-kernel@...r.kernel.org,
	Yinghai Lu <yinghai@...nel.org>, Ingo Molnar <mingo@...e.hu>
Subject: Re: [RFC] Correct behaviour of irq affinity?

On Tuesday 24 March 2009 23:09:37 Eric W. Biederman wrote:
> desc->affinity should be what the user requested, if it is at all
> possible to honor the user space request.  YH the fact that we do not
> currently exercise the full freedom that user space gives us is
> irrelevant.

Yep, OK.

> YH has a point that several of the implementations of
> cpu_mask_to_apic_id do not take cpu_online_map into account and should
> probably be fixed.  flat_cpu_mask_to_apicid was the one I could find.

Also the numaq apic.h.  I'll do an audit and send a patch.

> Also now that I look at it there is one other bug in this routine
> that you have missed.  set_extra_move_desc should be called before
> we set desc->affinity, as it compares that with the new value to
> see if we are going to be running on a new cpu, and if so we may
> need to reallocate irq_desc onto a new numa node.  set_extra_move_desc
> looks a little fishy but it doesn't stand a chance if it is called
> with the wrong data.

Yes, agree with Yinghai's fix.  I'll re-spin my patch on top of his.

Thanks for looking at this!
Rusty.
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