linux-kernel - Re: [PATCH 1/2] x86, irq: update irq_cfg domain unless the new affinity is a subset of the current domain

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Message-ID: <20120621110055.GE2223@dhcp-26-207.brq.redhat.com>
Date:	Thu, 21 Jun 2012 13:00:55 +0200
From:	Alexander Gordeev <agordeev@...hat.com>
To:	Suresh Siddha <suresh.b.siddha@...el.com>
Cc:	yinghai@...nel.org, linux-kernel@...r.kernel.org, x86@...nel.org,
	gorcunov@...nvz.org, Ingo Molnar <mingo@...nel.org>
Subject: Re: [PATCH 1/2] x86, irq: update irq_cfg domain unless the new
 affinity is a subset of the current domain

On Tue, Jun 19, 2012 at 05:18:42PM -0700, Suresh Siddha wrote:
> On Mon, 2012-06-18 at 17:51 -0700, Suresh Siddha wrote:
> BTW, there is still one open that I would like to address. How to handle
> the vector pressure during boot etc (as the default vector assignment
> specifies all online cpus) when there are lot interrupt sources but
> fewer x2apic clusters (like one or two socket server case).
> 
> We should be able to do something like the appended. Any better
> suggestions? I don't want to add boot parameters to limit the x2apic
> cluster membership etc (to fewer than 16 logical cpu's) if possible.

This cpu_online_mask approach should work IMO. Although it looks little bit
hacky for me. May be we could start with default_vector_allocation_domain()
and explicitly switch to cluster_vector_allocation_domain() once booted?

As of boot parameters, I can think of multi-pass walk thru a cpumask to find a
free cluster => core => sibling. In worst case I can imagine a vector space
defragmentator. But nothing really small to avoid current code reshake.

Also, how heavy the vector pressure actually is?

-- 
Regards,
Alexander Gordeev
agordeev@...hat.com
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