Re: [PATCH net-next v6 2/5] veth: implement Byte Queue Limits (BQL) for latency reduction

[Jesper Dangaard Brouer <hawk@kernel.org>]

On 04/06/2026 10.19, Paolo Abeni wrote:
> On 5/27/26 3:54 PM, hawk@kernel.org wrote:
>> @@ -348,10 +381,11 @@ static netdev_tx_t veth_xmit(struct sk_buff *skb, struct net_device *dev)
>>   {
>>   	struct veth_priv *rcv_priv, *priv = netdev_priv(dev);
>>   	struct veth_rq *rq = NULL;
>> -	struct netdev_queue *txq;
>> +	struct netdev_queue *txq = NULL;
> 
> Minor nit: please fix the variables declaration order above.
> 
>> @@ -1092,6 +1137,24 @@ static void veth_napi_del_range(struct net_device *dev, int start, int end)
>>   		ptr_ring_cleanup(&rq->xdp_ring, veth_ptr_free);
>>   	}
>>   
>> +	/* Reset BQL and wake stopped peer txqs.  A concurrent veth_xmit()
>> +	 * may have set DRV_XOFF between rcu_assign_pointer(napi, NULL) and
>> +	 * synchronize_net(), and NAPI can no longer clear it.
>> +	 * Only wake when the device is still up.
>> +	 */
>> +	peer = rtnl_dereference(priv->peer);
>> +	if (peer) {
>> +		int peer_end = min_t(int, end, peer->real_num_tx_queues);
> 
> Sashiko noted you may need to additionally complete/reset the tx queue
> in the <old_real_num_tx_queues> .. <new_real_num_tx_queue> range, and I
> think it's right.
> 

Trying a new approach in V7, that avoids calling reset. Instead, before
ptr_ring_cleanup(), consume any remaining packets and do the correct BQL
accounting.  Lets see if that pleases Sashiko ;-)

--Jesper