From 03f45c883c6f391ed4fff8292415b35bd1107519 Mon Sep 17 00:00:00 2001 From: Eric Dumazet Date: Mon, 16 Apr 2018 10:33:37 -0700 Subject: tcp: avoid extra wakeups for SO_RCVLOWAT users SO_RCVLOWAT is properly handled in tcp_poll(), so that POLLIN is only generated when enough bytes are available in receive queue, after David change (commit c7004482e8dc "tcp: Respect SO_RCVLOWAT in tcp_poll().") But TCP still calls sk->sk_data_ready() for each chunk added in receive queue, meaning thread is awaken, and goes back to sleep shortly after. Tested: tcp_mmap test program, receiving 32768 MB of data with SO_RCVLOWAT set to 512KB -> Should get ~2 wakeups (c-switches) per MB, regardless of how many (tiny or big) packets were received. High speed (mostly full size GRO packets) received 32768 MB (100 % mmap'ed) in 8.03112 s, 34.2266 Gbit, cpu usage user:0.037 sys:1.404, 43.9758 usec per MB, 65497 c-switches received 32768 MB (99.9954 % mmap'ed) in 7.98453 s, 34.4263 Gbit, cpu usage user:0.03 sys:1.422, 44.3115 usec per MB, 65485 c-switches Low speed (sender is ratelimited and sends 1-MSS at a time, so GRO is not helping) received 22474.5 MB (100 % mmap'ed) in 6015.35 s, 0.0313414 Gbit, cpu usage user:0.05 sys:1.586, 72.7952 usec per MB, 44950 c-switches Signed-off-by: Eric Dumazet Signed-off-by: David S. Miller --- include/net/tcp.h | 1 + 1 file changed, 1 insertion(+) (limited to 'include/net') diff --git a/include/net/tcp.h b/include/net/tcp.h index b2318242cad8..0ee85c47c185 100644 --- a/include/net/tcp.h +++ b/include/net/tcp.h @@ -403,6 +403,7 @@ void tcp_syn_ack_timeout(const struct request_sock *req); int tcp_recvmsg(struct sock *sk, struct msghdr *msg, size_t len, int nonblock, int flags, int *addr_len); int tcp_set_rcvlowat(struct sock *sk, int val); +void tcp_data_ready(struct sock *sk); void tcp_parse_options(const struct net *net, const struct sk_buff *skb, struct tcp_options_received *opt_rx, int estab, struct tcp_fastopen_cookie *foc); -- cgit v1.2.3