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

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Message-ID: <20190117204248-mutt-send-email-mst@kernel.org>
Date:   Thu, 17 Jan 2019 20:43:36 -0500
From:   "Michael S. Tsirkin" <mst@...hat.com>
To:     Willem de Bruijn <willemdebruijn.kernel@...il.com>
Cc:     netdev@...r.kernel.org, davem@...emloft.net, jasowang@...hat.com,
        Willem de Bruijn <willemb@...gle.com>,
        Mark Hlady <mhlady@...gle.com>
Subject: Re: [PATCH net-next] virtio-net: per-queue RPS config

On Thu, Jan 17, 2019 at 08:08:53PM -0500, Willem de Bruijn wrote:
> From: Willem de Bruijn <willemb@...gle.com>
> 
> 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 <mhlady@...gle.com>
> Signed-off-by: Willem de Bruijn <willemb@...gle.com>

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