netdev - Re: [PATCH net-next-2.6] sched: use xps information for qdisc NUMA affinity

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Message-Id: <20101130.112106.183035811.davem@davemloft.net>
Date:	Tue, 30 Nov 2010 11:21:06 -0800 (PST)
From:	David Miller <davem@...emloft.net>
To:	eric.dumazet@...il.com
Cc:	therbert@...gle.com, netdev@...r.kernel.org,
	bhutchings@...arflare.com, jesse.brandeburg@...el.com
Subject: Re: [PATCH net-next-2.6] sched: use xps information for qdisc NUMA
 affinity

From: Eric Dumazet <eric.dumazet@...il.com>
Date: Tue, 30 Nov 2010 20:07:27 +0100

[ Jesse CC:'d ]

> netdev struct itself is shared by all cpus, so there is no real choice,
> unless you know one netdev will be used by a restricted set of
> cpus/nodes... Probably very unlikely in practice.

Unfortunately Jesse has found non-trivial gains by NUMA localizing the
netdev struct during routing tests in soome configurations.

> We could change (only on NUMA setups maybe)
> 
> struct netdev_queue *_tx;
> 
> to a
> 
> struct netdev_queue **_tx;
> 
> and allocate each "struct netdev_queue" on appropriate node, but adding
> one indirection level might be overkill...
> 
> For very hot small structures, (one or two cache lines), I am not sure
> its worth the pain.

Jesse, do you think this would help the case you were testing?
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