Re: [dpdk-dev] [PATCH] net/af_xdp: fix Tx halt when no recv packets

[Ye Xiaolong <xiaolong.ye@intel.com>]

On 09/10, Zhang, Qi Z wrote:
>
>
>> -----Original Message-----
>> From: Ye, Xiaolong
>> Sent: Tuesday, September 10, 2019 12:13 AM
>> To: Yigit, Ferruh <ferruh.yigit@intel.com>; Loftus, Ciara
>> <ciara.loftus@intel.com>; Ye, Xiaolong <xiaolong.ye@intel.com>; Zhang, Qi Z
>> <qi.z.zhang@intel.com>
>> Cc: dev@dpdk.org; stable@dpdk.org
>> Subject: [PATCH] net/af_xdp: fix Tx halt when no recv packets
>> 
>> The kernel only consumes Tx packets if we have some Rx traffic on specified
>> queue or we have called send(). So we need to issue a send() even when the
>> allocation fails so that kernel will start to consume packets again.
>
>So "allocation fails" means " xsk_ring_prod__reserve" fail right?

Yes.

>I don't understand when xsk_ring_prod__needs_wakeup is true why kernel will stop Tx packet at this situation 
>would you share more insight?

Actually, the fail case is xsk_ring_prod__needs_wakeup is false, then we can't
issue a send() when xsk_ring_prod__reserve fails. 

Thanks,
Xiaolong

>
>Thanks
>Qi
>
>> 
>> Commit 45bba02c95b0 ("net/af_xdp: support need wakeup feature") breaks
>> above rule by adding some condition to send, this patch fixes it while still
>> keeps the need_wakeup feature for Tx.
>> 
>> Fixes: 45bba02c95b0 ("net/af_xdp: support need wakeup feature")
>> Cc: stable@dpdk.org
>> 
>> Signed-off-by: Xiaolong Ye <xiaolong.ye@intel.com>
>> ---
>>  drivers/net/af_xdp/rte_eth_af_xdp.c | 28 ++++++++++++++--------------
>>  1 file changed, 14 insertions(+), 14 deletions(-)
>> 
>> diff --git a/drivers/net/af_xdp/rte_eth_af_xdp.c
>> b/drivers/net/af_xdp/rte_eth_af_xdp.c
>> index 41ed5b2af..e496e9aaa 100644
>> --- a/drivers/net/af_xdp/rte_eth_af_xdp.c
>> +++ b/drivers/net/af_xdp/rte_eth_af_xdp.c
>> @@ -286,19 +286,16 @@ kick_tx(struct pkt_tx_queue *txq)  {
>>  	struct xsk_umem_info *umem = txq->pair->umem;
>> 
>> -#if defined(XDP_USE_NEED_WAKEUP)
>> -	if (xsk_ring_prod__needs_wakeup(&txq->tx))
>> -#endif
>> -		while (send(xsk_socket__fd(txq->pair->xsk), NULL,
>> -			    0, MSG_DONTWAIT) < 0) {
>> -			/* some thing unexpected */
>> -			if (errno != EBUSY && errno != EAGAIN && errno != EINTR)
>> -				break;
>> -
>> -			/* pull from completion queue to leave more space */
>> -			if (errno == EAGAIN)
>> -				pull_umem_cq(umem, ETH_AF_XDP_TX_BATCH_SIZE);
>> -		}
>> +	while (send(xsk_socket__fd(txq->pair->xsk), NULL,
>> +		    0, MSG_DONTWAIT) < 0) {
>> +		/* some thing unexpected */
>> +		if (errno != EBUSY && errno != EAGAIN && errno != EINTR)
>> +			break;
>> +
>> +		/* pull from completion queue to leave more space */
>> +		if (errno == EAGAIN)
>> +			pull_umem_cq(umem, ETH_AF_XDP_TX_BATCH_SIZE);
>> +	}
>>  	pull_umem_cq(umem, ETH_AF_XDP_TX_BATCH_SIZE);  }
>> 
>> @@ -367,7 +364,10 @@ eth_af_xdp_tx(void *queue, struct rte_mbuf
>> **bufs, uint16_t nb_pkts)
>> 
>>  	xsk_ring_prod__submit(&txq->tx, nb_pkts);
>> 
>> -	kick_tx(txq);
>> +#if defined(XDP_USE_NEED_WAKEUP)
>> +	if (xsk_ring_prod__needs_wakeup(&txq->tx))
>> +#endif
>> +		kick_tx(txq);
>> 
>>  	txq->stats.tx_pkts += nb_pkts;
>>  	txq->stats.tx_bytes += tx_bytes;
>> --
>> 2.17.1
>