netdev - Re: [PATCH] [PATCH net-next] tun: fix multiqueue rx

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Message-ID: <20181116150952-mutt-send-email-mst@kernel.org>
Date:   Fri, 16 Nov 2018 15:10:21 -0500
From:   "Michael S. Tsirkin" <mst@...hat.com>
To:     Matthew Cover <werekraken@...il.com>
Cc:     davem@...emloft.net, jasowang@...hat.com, brouer@...hat.com,
        edumazet@...gle.com, sd@...asysnail.net, netdev@...r.kernel.org,
        matthew.cover@...ckpath.com
Subject: Re: [PATCH] [PATCH net-next] tun: fix multiqueue rx

On Fri, Nov 16, 2018 at 12:00:15AM -0700, Matthew Cover wrote:
> When writing packets to a descriptor associated with a combined queue, the
> packets should end up on that queue.
> 
> Before this change all packets written to any descriptor associated with a
> tap interface end up on rx-0, even when the descriptor is associated with a
> different queue.
> 
> The rx traffic can be generated by either of the following.
>   1. a simple tap program which spins up multiple queues and writes packets
>      to each of the file descriptors
>   2. tx from a qemu vm with a tap multiqueue netdev
> 
> The queue for rx traffic can be observed by either of the following (done
> on the hypervisor in the qemu case).
>   1. a simple netmap program which opens and reads from per-queue
>      descriptors
>   2. configuring RPS and doing per-cpu captures with rxtxcpu
> 
> Alternatively, if you printk() the return value of skb_get_rx_queue() just
> before each instance of netif_receive_skb() in tun.c, you will get 65535
> for every skb.
> 
> Calling skb_record_rx_queue() to set the rx queue to the queue_index fixes
> the association between descriptor and rx queue.
> 
> Signed-off-by: Matthew Cover <matthew.cover@...ckpath.com>

Acked-by: Michael S. Tsirkin <mst@...hat.com>

stable material?

> ---
>  drivers/net/tun.c | 7 ++++++-
>  1 file changed, 6 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/net/tun.c b/drivers/net/tun.c
> index a65779c6d72f..ce8620f3ea5e 100644
> --- a/drivers/net/tun.c
> +++ b/drivers/net/tun.c
> @@ -1536,6 +1536,7 @@ static void tun_rx_batched(struct tun_struct *tun, struct tun_file *tfile,
>  
>  	if (!rx_batched || (!more && skb_queue_empty(queue))) {
>  		local_bh_disable();
> +		skb_record_rx_queue(skb, tfile->queue_index);
>  		netif_receive_skb(skb);
>  		local_bh_enable();
>  		return;
> @@ -1555,8 +1556,11 @@ static void tun_rx_batched(struct tun_struct *tun, struct tun_file *tfile,
>  		struct sk_buff *nskb;
>  
>  		local_bh_disable();
> -		while ((nskb = __skb_dequeue(&process_queue)))
> +		while ((nskb = __skb_dequeue(&process_queue))) {
> +			skb_record_rx_queue(nskb, tfile->queue_index);
>  			netif_receive_skb(nskb);
> +		}
> +		skb_record_rx_queue(skb, tfile->queue_index);
>  		netif_receive_skb(skb);
>  		local_bh_enable();
>  	}
> @@ -2452,6 +2456,7 @@ static int tun_xdp_one(struct tun_struct *tun,
>  	    !tfile->detached)
>  		rxhash = __skb_get_hash_symmetric(skb);
>  
> +	skb_record_rx_queue(skb, tfile->queue_index);
>  	netif_receive_skb(skb);
>  
>  	stats = get_cpu_ptr(tun->pcpu_stats);
> -- 
> 2.15.2 (Apple Git-101.1)