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tcp: batch calls to sk_flush_backlog() 

Starting from commit d41a69f1d3 ("tcp: make tcp_sendmsg() aware of socket backlog")
loopback flows got hurt, because for each skb sent, the socket receives an
immediate ACK and sk_flush_backlog() causes extra work.

Intent was to not let the backlog grow too much, but we went a bit too far.

We can check the backlog every 16 skbs (about 1MB chunks)
to increase TCP over loopback performance by about 15 %

Note that the call to sk_flush_backlog() handles a single ACK,
thanks to coalescing done on backlog, but cleans the 16 skbs
found in rtx rb-tree.

Reported-by: Soheil Hassas Yeganeh <soheil@google.com>
Signed-off-by: Eric Dumazet <edumazet@google.com>
Acked-by: Soheil Hassas Yeganeh <soheil@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
This commit is contained in:
Eric Dumazet 2019-08-09 05:04:47 -07:00 committed by David S. Miller
parent fcc32a2165
commit 1a9914884d
1 changed files with 6 additions and 5 deletions
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11
net/ipv4/tcp.c
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@ -1162,7 +1162,7 @@ int tcp_sendmsg_locked(struct sock *sk, struct msghdr *msg, size_t size)
struct sockcm_cookie sockc;
int flags, err, copied = 0;
int mss_now = 0, size_goal, copied_syn = 0;
bool process_backlog = false;
int process_backlog = 0;
bool zc = false;
long timeo;
@ -1254,9 +1254,10 @@ new_segment:
if (!sk_stream_memory_free(sk))
goto wait_for_sndbuf;
if (process_backlog && sk_flush_backlog(sk)) {
process_backlog = false;
goto restart;
if (unlikely(process_backlog >= 16)) {
process_backlog = 0;
if (sk_flush_backlog(sk))
goto restart;
}
first_skb = tcp_rtx_and_write_queues_empty(sk);
skb = sk_stream_alloc_skb(sk, 0, sk->sk_allocation,
@ -1264,7 +1265,7 @@ new_segment:
if (!skb)
goto wait_for_memory;
process_backlog = true;
process_backlog++;
skb->ip_summed = CHECKSUM_PARTIAL;
skb_entail(sk, skb);