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From 75eefc6c59fd2c5f1ab95a3a113c217237d12a31 Mon Sep 17 00:00:00 2001
From: Eric Dumazet <edumazet@google.com>
Date: Sat, 3 Dec 2016 11:14:54 -0800
Subject: [PATCH 05/10] tcp: tsq: add a shortcut in tcp_small_queue_check()
Always allow the two first skbs in write queue to be sent,
regardless of sk_wmem_alloc/sk_pacing_rate values.
This helps a lot in situations where TX completions are delayed either
because of driver latencies or softirq latencies.
Test is done with no cache line misses.
Signed-off-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
---
net/ipv4/tcp_output.c | 9 +++++++++
1 file changed, 9 insertions(+)
--- a/net/ipv4/tcp_output.c
+++ b/net/ipv4/tcp_output.c
@@ -2142,6 +2142,15 @@ static bool tcp_small_queue_check(struct
limit <<= factor;
if (atomic_read(&sk->sk_wmem_alloc) > limit) {
+ /* Always send the 1st or 2nd skb in write queue.
+ * No need to wait for TX completion to call us back,
+ * after softirq/tasklet schedule.
+ * This helps when TX completions are delayed too much.
+ */
+ if (skb == sk->sk_write_queue.next ||
+ skb->prev == sk->sk_write_queue.next)
+ return false;
+
set_bit(TSQ_THROTTLED, &tcp_sk(sk)->tsq_flags);
/* It is possible TX completion already happened
* before we set TSQ_THROTTLED, so we must
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