Subject: Re: [PATCH net-next] virtio-net: per-queue RPS config

From: "Michael S. Tsirkin" <[email-masked]>
Date: Thu, 17 Jan 2019 20:43:36 -0500

On Thu, Jan 17, 2019 at 08:08:53PM -0500, Willem de Bruijn wrote:
> From: Willem de Bruijn <[email-masked]>
> 
> On multiqueue network devices, RPS maps are configured independently
> for each receive queue through /sys/class/net/$DEV/queues/rx-*.
> 
> On virtio-net currently all packets use the map from rx-0, because the
> real rx queue is not known at time of map lookup by get_rps_cpu.
> 
> Call skb_record_rx_queue in the driver rx path to make lookup work.
> 
> Recording the receive queue has ramifications beyond RPS, such as in
> sticky load balancing decisions for sockets (skb_tx_hash) and XPS.
> 
> Reported-by: Mark Hlady <[email-masked]>
> Signed-off-by: Willem de Bruijn <[email-masked]>

And any examples how to see the benefit of this?

> ---
>  drivers/net/virtio_net.c | 1 +
>  1 file changed, 1 insertion(+)
> 
> diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
> index 0237250860467..236ba5d5fb4bb 100644
> --- a/drivers/net/virtio_net.c
> +++ b/drivers/net/virtio_net.c
> @@ -1035,6 +1035,7 @@ static void receive_buf(struct virtnet_info *vi, struct receive_queue *rq,
>  		goto frame_err;
>  	}
>  
> +	skb_record_rx_queue(skb, vq2rxq(rq->vq));
>  	skb->protocol = eth_type_trans(skb, dev);
>  	pr_debug("Receiving skb proto 0x%04x len %i type %i\n",
>  		 ntohs(skb->protocol), skb->len, skb->pkt_type);
> -- 
> 2.20.1.321.g9e740568ce-goog