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

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Date:	Tue, 24 Nov 2009 14:05:43 -0800
From:	Peter P Waskiewicz Jr <peter.p.waskiewicz.jr@...el.com>
To:	Thomas Gleixner <tglx@...utronix.de>
Cc:	David Miller <davem@...emloft.net>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"arjan@...ux.jf.intel.com" <arjan@...ux.jf.intel.com>,
	"mingo@...e.hu" <mingo@...e.hu>,
	"yong.zhang0@...il.com" <yong.zhang0@...il.com>,
	"netdev@...r.kernel.org" <netdev@...r.kernel.org>
Subject: Re: [PATCH v2] irq: Add node_affinity CPU masks for smarter
 irqbalance hints

On Tue, 2009-11-24 at 13:56 -0800, Thomas Gleixner wrote:
> 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 ?
> 

Just to clarify, I need a preferred CPU mask on a per IRQ basis.  And
yes, that mask may not be restricted to the CPUs of a single NUMA node.
But in the normal case, the mask will be restricted to CPUs of a single
node.

Cheers,
-PJ

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