Re: [PATCH net-next v2] virtio-net: xsk: Support wakeup on RX side

[Bui Quang Minh <minhquangbui99@gmail.com>]

On 3/3/26 01:53, Michael S. Tsirkin wrote:
> On Mon, Mar 02, 2026 at 11:41:58PM +0700, Bui Quang Minh wrote:
>> When XDP_USE_NEED_WAKEUP is used and the fill ring is empty so no buffer
>> is allocated on RX side, allow RX NAPI to be descheduled. This avoids
>> wasting CPU cycles on polling. Users will be notified and they need to
>> make a wakeup call after refilling the ring.
>>
>> Signed-off-by: Bui Quang Minh <minhquangbui99@gmail.com>
>> ---
>> Changes in v2:
>> - Fix the flag check in virtnet_xsk_wakeup
>> - Link to v1: https://lore.kernel.org/netdev/20260227150949.13089-1-minhquangbui99@gmail.com/
>> ---
>>   drivers/net/virtio_net.c | 35 +++++++++++++++++++++++++++--------
>>   1 file changed, 27 insertions(+), 8 deletions(-)
>>
>> diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
>> index db88dcaefb20..3614002fc87c 100644
>> --- a/drivers/net/virtio_net.c
>> +++ b/drivers/net/virtio_net.c
>> @@ -1454,8 +1454,19 @@ static int virtnet_add_recvbuf_xsk(struct virtnet_info *vi, struct receive_queue
>>   	xsk_buffs = rq->xsk_buffs;
>>   
>>   	num = xsk_buff_alloc_batch(pool, xsk_buffs, rq->vq->num_free);
>> -	if (!num)
>> +	if (!num) {
>> +		if (xsk_uses_need_wakeup(pool)) {
>> +			xsk_set_rx_need_wakeup(pool);
>> +			/* Return 0 instead of -ENOMEM so that NAPI is
>> +			 * descheduled.
>> +			 */
>> +			return 0;
> With this change, try_fill_recv() can return true even though zero RX
> buffers were posted in need_wakeup mode, which contradicts its
> documentation ("Returns false if we couldn't fill entirely (OOM)").
>
> Methinks we need to at least update the comment near try_fill_recv.

I'll update the comment of try_fill_recv function.

Thanks,
Quang Minh.

>
>
>
>> +		}
>> +
>>   		return -ENOMEM;
>> +	} else {
>> +		xsk_clear_rx_need_wakeup(pool);
>> +	}
>>   
>>   	len = xsk_pool_get_rx_frame_size(pool) + vi->hdr_len;
>>   
>> @@ -1588,20 +1599,19 @@ static bool virtnet_xsk_xmit(struct send_queue *sq, struct xsk_buff_pool *pool,
>>   	return sent;
>>   }
>>   
>> -static void xsk_wakeup(struct send_queue *sq)
>> +static void xsk_wakeup(struct napi_struct *napi, struct virtqueue *vq)
>>   {
>> -	if (napi_if_scheduled_mark_missed(&sq->napi))
>> +	if (napi_if_scheduled_mark_missed(napi))
>>   		return;
>>   
>>   	local_bh_disable();
>> -	virtqueue_napi_schedule(&sq->napi, sq->vq);
>> +	virtqueue_napi_schedule(napi, vq);
>>   	local_bh_enable();
>>   }
>>   
>>   static int virtnet_xsk_wakeup(struct net_device *dev, u32 qid, u32 flag)
>>   {
>>   	struct virtnet_info *vi = netdev_priv(dev);
>> -	struct send_queue *sq;
>>   
>>   	if (!netif_running(dev))
>>   		return -ENETDOWN;
>> @@ -1609,9 +1619,18 @@ static int virtnet_xsk_wakeup(struct net_device *dev, u32 qid, u32 flag)
>>   	if (qid >= vi->curr_queue_pairs)
>>   		return -EINVAL;
>>   
>> -	sq = &vi->sq[qid];
>> +	if (flag & XDP_WAKEUP_TX) {
>> +		struct send_queue *sq = &vi->sq[qid];
>> +
>> +		xsk_wakeup(&sq->napi, sq->vq);
>> +	}
>> +
>> +	if (flag & XDP_WAKEUP_RX) {
>> +		struct receive_queue *rq = &vi->rq[qid];
>> +
>> +		xsk_wakeup(&rq->napi, rq->vq);
>> +	}
>>   
>> -	xsk_wakeup(sq);
>>   	return 0;
>>   }
>>   
>> @@ -1623,7 +1642,7 @@ static void virtnet_xsk_completed(struct send_queue *sq, int num)
>>   	 * wakeup the tx napi to consume the xsk tx queue, because the tx
>>   	 * interrupt may not be triggered.
>>   	 */
>> -	xsk_wakeup(sq);
>> +	xsk_wakeup(&sq->napi, sq->vq);
>>   }
>>   
>>   static int __virtnet_xdp_xmit_one(struct virtnet_info *vi,
>> -- 
>> 2.43.0