netdev - Re: [RFC] export irq_set/get_affinity() for multiqueue network drivers

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Message-ID: <8763pjpy2b.fsf@basil.nowhere.org>
Date:	Fri, 29 Aug 2008 18:48:12 +0200
From:	Andi Kleen <andi@...stfloor.org>
To:	Arjan van de Ven <arjan@...radead.org>
Cc:	Brice Goglin <Brice.Goglin@...ia.fr>,
	LKML <linux-kernel@...r.kernel.org>, netdev@...r.kernel.org
Subject: Re: [RFC] export irq_set/get_affinity() for multiqueue network drivers

Arjan van de Ven <arjan@...radead.org> writes:

> On Thu, 28 Aug 2008 22:21:53 +0200
> Brice Goglin <Brice.Goglin@...ia.fr> wrote:
>
>> Hello,
>> 
>> Is there any way to setup IRQ masks from within a driver? myri10ge
>> currently relies on an external script (writing in
>> /proc/irq/*/smp_affinity) to bind each queue/MSI-X to a different
>> processor. By default, Linux will either:
>> * round-robin the interrupts (killing the benefit of DCA for instance)
>> * put all IRQs on the same CPU (killing much of th
>
> * do the right thing with the userspace irq balancer

It probably also needs to be hooked up the sched_mc_power_savings
When the switch is on the interrupts shouldn't be spread out over
that many sockets.

Does it need callbacks to change the interrupts when that variable
changes?

Also I suspect handling SMT explicitely is a good idea. e.g. I would
always set the affinity to all thread siblings in a core, not 
just a single one, because context switch is very cheap between them.

-Andi

-- 
ak@...ux.intel.com
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