netdev - Re: [net-next RFC V5 5/5] virtio_net: support negotiating the number of queues through ctrl vq

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Message-ID: <1341864803.2535.53.camel@bwh-desktop.uk.solarflarecom.com>
Date:	Mon, 9 Jul 2012 21:13:23 +0100
From:	Ben Hutchings <bhutchings@...arflare.com>
To:	Jason Wang <jasowang@...hat.com>
CC:	<mst@...hat.com>, <mashirle@...ibm.com>, <krkumar2@...ibm.com>,
	<habanero@...ux.vnet.ibm.com>, <rusty@...tcorp.com.au>,
	<netdev@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
	<virtualization@...ts.linux-foundation.org>, <edumazet@...gle.com>,
	<tahm@...ux.vnet.ibm.com>, <jwhan@...ewood.snu.ac.kr>,
	<davem@...emloft.net>, <akong@...hat.com>, <kvm@...r.kernel.org>,
	<sri@...ibm.com>
Subject: Re: [net-next RFC V5 5/5] virtio_net: support negotiating the
 number of queues through ctrl vq

On Thu, 2012-07-05 at 18:29 +0800, Jason Wang wrote:
> This patch let the virtio_net driver can negotiate the number of queues it
> wishes to use through control virtqueue and export an ethtool interface to let
> use tweak it.
> 
> As current multiqueue virtio-net implementation has optimizations on per-cpu
> virtuqueues, so only two modes were support:
> 
> - single queue pair mode
> - multiple queue paris mode, the number of queues matches the number of vcpus
> 
> The single queue mode were used by default currently due to regression of
> multiqueue mode in some test (especially in stream test).
> 
> Since virtio core does not support paritially deleting virtqueues, so during
> mode switching the whole virtqueue were deleted and the driver would re-create
> the virtqueues it would used.
> 
> btw. The queue number negotiating were defered to .ndo_open(), this is because
> only after feature negotitaion could we send the command to control virtqueue
> (as it may also use event index).
[...]
> +static int virtnet_set_channels(struct net_device *dev,
> +				struct ethtool_channels *channels)
> +{
> +	struct virtnet_info *vi = netdev_priv(dev);
> +	u16 queues = channels->rx_count;
> +	unsigned status = VIRTIO_CONFIG_S_ACKNOWLEDGE | VIRTIO_CONFIG_S_DRIVER;
> +
> +	if (channels->rx_count != channels->tx_count)
> +		return -EINVAL;
[...]
> +static void virtnet_get_channels(struct net_device *dev,
> +				 struct ethtool_channels *channels)
> +{
> +	struct virtnet_info *vi = netdev_priv(dev);
> +
> +	channels->max_rx = vi->total_queue_pairs;
> +	channels->max_tx = vi->total_queue_pairs;
> +	channels->max_other = 0;
> +	channels->max_combined = 0;
> +	channels->rx_count = vi->num_queue_pairs;
> +	channels->tx_count = vi->num_queue_pairs;
> +	channels->other_count = 0;
> +	channels->combined_count = 0;
> +}
[...]

It looks like the queue-pairs should be treated as 'combined channels',
not separate RX and TX channels.  Also you don't need to clear the other
members; you can assume that the ethtool core will zero-initialise
structures for 'get' operations.

Ben.

-- 
Ben Hutchings, Staff Engineer, Solarflare
Not speaking for my employer; that's the marketing department's job.
They asked us to note that Solarflare product names are trademarked.

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