netdev - Re: [PATCH net-next 3/3] virtio-net: change the number of queues through ethtool

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Date:	Tue, 4 Dec 2012 15:49:59 +0200
From:	"Michael S. Tsirkin" <mst@...hat.com>
To:	Jason Wang <jasowang@...hat.com>
Cc:	rusty@...tcorp.com.au, virtualization@...ts.linux-foundation.org,
	netdev@...r.kernel.org, linux-kernel@...r.kernel.org,
	davem@...emloft.net, krkumar2@...ibm.com, kvm@...r.kernel.org,
	bhutchings@...arflare.com, jwhan@...ewood.snu.ac.kr,
	shiyer@...hat.com
Subject: Re: [PATCH net-next 3/3] virtio-net: change the number of queues
 through ethtool

On Tue, Dec 04, 2012 at 07:07:58PM +0800, Jason Wang wrote:
> This patch implement the ethtool_{set|get}_channels method of ethool to allow
> user to change the number of queues dymaically when the device is running. This
> would let the user to configure it on demand.
> 
> Signed-off-by: Jason Wang <jasowang@...hat.com>
> ---
>  drivers/net/virtio_net.c |   44 ++++++++++++++++++++++++++++++++++++++++++++
>  1 files changed, 44 insertions(+), 0 deletions(-)
> 
> diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
> index 912f5b2..b9f9887 100644
> --- a/drivers/net/virtio_net.c
> +++ b/drivers/net/virtio_net.c
> @@ -1589,10 +1589,54 @@ static struct virtio_driver virtio_net_driver = {
>  #endif
>  };
>  
> +/* TODO: Eliminate OOO packets during switching */
> +static int virtnet_set_channels(struct net_device *dev,
> +				struct ethtool_channels *channels)
> +{
> +	struct virtnet_info *vi = netdev_priv(dev);
> +	u16 queue_pairs = channels->combined_count;
> +	u16 old_queue_pairs = vi->curr_queue_pairs;
> +
> +	/* We don't support separate rx/tx channels.
> +	 * We don't allow setting 'other' channels.
> +	 */
> +	if (channels->rx_count || channels->tx_count || channels->other_count)
> +		return -EINVAL;
> +
> +	if (queue_pairs > vi->max_queue_pairs)
> +		return -EINVAL;
> +
> +	vi->curr_queue_pairs = queue_pairs;
> +	if (virtnet_set_queues(vi) == 0) {
> +		netif_set_real_num_tx_queues(dev, vi->curr_queue_pairs);
> +		netif_set_real_num_rx_queues(dev, vi->curr_queue_pairs);

Just use queue_pairs - it's shorter.

> +
> +		virtnet_set_affinity(vi, true);
> +	} else
> +		vi->curr_queue_pairs = old_queue_pairs;

Should be
	ret = virtnet_set_queues(vi);
	if (ret) {
		vi->curr_queue_pairs = old_queue_pairs;
		return ret;
	}
otherwise we loose error reporting.

Also it's better if virtnet_set_queues
gets queue_pairs as parameter and set curr_queue_pairs
on success.

> +
> +	return 0;
> +}
> +
> +static void virtnet_get_channels(struct net_device *dev,
> +				 struct ethtool_channels *channels)
> +{
> +	struct virtnet_info *vi = netdev_priv(dev);
> +
> +	channels->combined_count = vi->curr_queue_pairs;
> +	channels->max_combined = vi->max_queue_pairs;
> +	channels->max_other = 0;
> +	channels->rx_count = 0;
> +	channels->tx_count = 0;
> +	channels->other_count = 0;
> +}
> +
>  static const struct ethtool_ops virtnet_ethtool_ops = {
>  	.get_drvinfo = virtnet_get_drvinfo,
>  	.get_link = ethtool_op_get_link,
>  	.get_ringparam = virtnet_get_ringparam,
> +	.set_channels = virtnet_set_channels,
> +	.get_channels = virtnet_get_channels,
>  };
>  
>  static int __init init(void)
> -- 
> 1.7.1
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