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

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Date:	Tue, 24 Nov 2009 09:57:03 -0800 (PST)
From:	David Miller <davem@...emloft.net>
To:	tglx@...utronix.de
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

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.
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