Re: [Linux-stable-mirror] [PATCH] net: mvneta: fix handling of the Tx descriptor counter

11 Nov 2017


      From: Simon Guinot simon.guinot@sequanux.org
Date: Wed,  8 Nov 2017 17:58:35 +0100
...
@@ -2413,8 +2416,7 @@ static int mvneta_tx(struct sk_buff *skb, struct net_device *dev)
   	if (txq->count >= txq->tx_stop_threshold)
   		netif_tx_stop_queue(nq);

if (!skb->xmit_more || netif_xmit_stopped(nq) ||


    txq->pending + frags > MVNETA_TXQ_DEC_SENT_MASK)




if (!skb->xmit_more || netif_xmit_stopped(nq))
mvneta_txq_pend_desc_add(pp, txq, frags);

else
	txq->pending += frags;

As David Laight said, you should not allow unlimited amounts of
->xmit_more frames to be queued without a TX doorbell update.
Therefore, please keep some kind of limit here otherwise latency
will spike in some circumstances.

    