linux-kernel - Re: [PATCH v2] irq: Add node_affinity CPU masks for smarter irqbalance hints

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Date:	Tue, 24 Nov 2009 22:56:29 +0100 (CET)
From:	Thomas Gleixner <tglx@...utronix.de>
To:	David Miller <davem@...emloft.net>
cc:	peter.p.waskiewicz.jr@...el.com, linux-kernel@...r.kernel.org,
	arjan@...ux.jf.intel.com, mingo@...e.hu, yong.zhang0@...il.com,
	netdev@...r.kernel.org
Subject: Re: [PATCH v2] irq: Add node_affinity CPU masks for smarter irqbalance
 hints

On Tue, 24 Nov 2009, David Miller wrote:

> From: Thomas Gleixner <tglx@...utronix.de>
> Date: Tue, 24 Nov 2009 12:07:35 +0100 (CET)
> 
> > And what does the kernel do with this information and why are we not
> > using the existing device/numa_node information ?
> 
> It's a different problem space Thomas.
> 
> If the device lives on NUMA node X, we still end up wanting to
> allocate memory resources (RX ring buffers) on other NUMA nodes on a
> per-queue basis.
> 
> Otherwise a network card's forwarding performance is limited by the
> memory bandwidth of a single NUMA node, and on a multiqueue cards we
> therefore fare much better by allocating each device RX queue's memory
> resources on a different NUMA node.
> 
> It is this NUMA usage that PJ is trying to export somehow to userspace
> so that irqbalanced and friends can choose the IRQ cpu masks more
> intelligently.

So you need a preferred irq mask information on a per IRQ basis and
that mask is not restricted to the CPUs of a single NUMA node, right ?

Thanks,

	tglx



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