linux-kernel - Re: [net-next PATCH V2] virtio-net: switch to use XPS to choose txq

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Message-Id: <20130930.221040.543720988967287293.davem@davemloft.net>
Date:	Mon, 30 Sep 2013 22:10:40 -0700 (PDT)
From:	David Miller <davem@...emloft.net>
To:	jasowang@...hat.com
Cc:	rusty@...tcorp.com.au, mst@...hat.com,
	virtualization@...ts.linux-foundation.org, netdev@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [net-next PATCH V2] virtio-net: switch to use XPS to choose txq

From: Jason Wang <jasowang@...hat.com>
Date: Mon, 30 Sep 2013 15:37:17 +0800

> We used to use a percpu structure vq_index to record the cpu to queue
> mapping, this is suboptimal since it duplicates the work of XPS and
> loses all other XPS functionality such as allowing use to configure
> their own transmission steering strategy.
> 
> So this patch switches to use XPS and suggest a default mapping when
> the number of cpus is equal to the number of queues. With XPS support,
> there's no need for keeping per-cpu vq_index and .ndo_select_queue(),
> so they were removed also.
> 
> Cc: Rusty Russell <rusty@...tcorp.com.au>
> Cc: Michael S. Tsirkin <mst@...hat.com>
> Signed-off-by: Jason Wang <jasowang@...hat.com>
> ---
> Changes from V1:
> - use cpumask_of() instead of allocate dynamically

This generates build warnings:

drivers/net/virtio_net.c: In function ‘virtnet_set_affinity’:
drivers/net/virtio_net.c:1093:3: warning: passing argument 2 of ‘netif_set_xps_queue’ discards ‘const’ qualifier from pointer target type [enabled by default]
In file included from drivers/net/virtio_net.c:20:0:
include/linux/netdevice.h:2275:5: note: expected ‘struct cpumask *’ but argument is of type ‘const struct cpumask *’