netdev - [PATCH v2 net 2/3] net: do not abort bulk send on BQL status

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Message-Id: <20181031153914.132127-3-edumazet@google.com>
Date:   Wed, 31 Oct 2018 08:39:13 -0700
From:   Eric Dumazet <edumazet@...gle.com>
To:     "David S . Miller" <davem@...emloft.net>
Cc:     netdev <netdev@...r.kernel.org>,
        Tariq Toukan <tariqt@...lanox.com>,
        Willem de Bruijn <willemb@...gle.com>,
        Eric Dumazet <edumazet@...gle.com>,
        Eric Dumazet <eric.dumazet@...il.com>
Subject: [PATCH v2 net 2/3] net: do not abort bulk send on BQL status

Before calling dev_hard_start_xmit(), upper layers tried
to cook optimal skb list based on BQL budget.

Problem is that GSO packets can end up comsuming more than
the BQL budget.

Breaking the loop is not useful, since requeued packets
are ahead of any packets still in the qdisc.

It is also more expensive, since next TX completion will
push these packets later, while skbs are not in cpu caches.

It is also a behavior difference with TSO packets, that can
break the BQL limit by a large amount.

Note that drivers should use __netdev_tx_sent_queue()
in order to have optimal xmit_more support, and avoid
useless atomic operations as shown in the following patch.

Signed-off-by: Eric Dumazet <edumazet@...gle.com>
---
 net/core/dev.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/net/core/dev.c b/net/core/dev.c
index 77d43ae2a7bbe1267f8430d5c35637d1984f463c..0ffcbdd55fa9ee545c807f2ed3fc178830e3075a 100644
--- a/net/core/dev.c
+++ b/net/core/dev.c
@@ -3272,7 +3272,7 @@ struct sk_buff *dev_hard_start_xmit(struct sk_buff *first, struct net_device *de
 		}

 		skb = next;
-		if (netif_xmit_stopped(txq) && skb) {
+		if (netif_tx_queue_stopped(txq) && skb) {
 			rc = NETDEV_TX_BUSY;
 			break;
 		}
-- 
2.19.1.930.g4563a0d9d0-goog