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| author |   Florian Westphal <fw@strlen.de> | 2017-08-30 19:24:58 +0200 |
|---|---|---|
| committer |   David S. Miller <davem@davemloft.net> | 2017-08-30 11:20:09 -0700 |
| commit | 31770e34e43d6c8dee129bfee77e56c34e61f0e5 (patch) | |
| tree | a4635a632732b39ef560a8f72eb3a81d04f01605 /net/ipv4/tcp_output.c | |
| parent | tcp: Revert "tcp: remove CA_ACK_SLOWPATH" (diff) | |
| download | linux-dev-31770e34e43d6c8dee129bfee77e56c34e61f0e5.tar.xz linux-dev-31770e34e43d6c8dee129bfee77e56c34e61f0e5.zip | |
tcp: Revert "tcp: remove header prediction"
This reverts commit 45f119bf936b1f9f546a0b139c5b56f9bb2bdc78.
Eric Dumazet says:
We found at Google a significant regression caused by
45f119bf936b1f9f546a0b139c5b56f9bb2bdc78 tcp: remove header prediction
In typical RPC (TCP_RR), when a TCP socket receives data, we now call
tcp_ack() while we used to not call it.
This touches enough cache lines to cause a slowdown.
so problem does not seem to be HP removal itself but the tcp_ack()
call. Therefore, it might be possible to remove HP after all, provided
one finds a way to elide tcp_ack for most cases.
Reported-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: Florian Westphal <fw@strlen.de>
Signed-off-by: David S. Miller <davem@davemloft.net>
Diffstat (limited to 'net/ipv4/tcp_output.c')
| -rw-r--r-- | net/ipv4/tcp_output.c | 2 |
1 files changed, 2 insertions, 0 deletions
diff --git a/net/ipv4/tcp_output.c b/net/ipv4/tcp_output.c index 3e0d19631534..5b6690d05abb 100644 --- a/net/ipv4/tcp_output.c +++ b/net/ipv4/tcp_output.c @@ -295,7 +295,9 @@ static u16 tcp_select_window(struct sock *sk) /* RFC1323 scaling applied */ new_win >>= tp->rx_opt.rcv_wscale; + /* If we advertise zero window, disable fast path. */ if (new_win == 0) { + tp->pred_flags = 0; if (old_win) NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPTOZEROWINDOWADV); |