netdev - Re: [PATCH net-next 01/12] net/mlx4_en: Reuse mapped memory in RX flow

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Date:	Mon, 09 Dec 2013 07:17:16 -0800
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Amir Vadai <amirv@...lanox.com>
Cc:	"David S. Miller" <davem@...emloft.net>,
	Or Gerlitz <ogerlitz@...lanox.com>,
	Yevgeny Petrilin <yevgenyp@...lanox.com>,
	netdev@...r.kernel.org, Eugenia Emantayev <eugenia@...lanox.com>
Subject: Re: [PATCH net-next 01/12] net/mlx4_en: Reuse mapped memory in RX
 flow

On Mon, 2013-12-09 at 11:44 +0200, Amir Vadai wrote:

> We get optimal performance when rx rings are mapped 1:1 to cpu's - IRQ
> affinity is set to this CPU, and memory is allocated on the NUMA node
> close to it (ring->numa_node)
> In order to do that, we will post a patch soon to use
> irq_set_affinity_hint() in order to hint the irq balancer. Till this
> patch is applied, users should set irq affinity through sysfs and
> disable the irq balancer.

Point is : You have nothing to do to affine memory allocations.

The big problem is correct IRQ affinity, which as you said is addressed
in a different way/patch

If the IRQ is properly setup, automatically or by irq affinities,
then memory will be allocated on the right node, its properly done
by all memory allocators.

The xxx_alloc_node() variants in the fast path are therefore not needed,
and not using them avoids catastrophic results if affinities are not
properly set.


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