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authorJosh Hunt <johunt@akamai.com>2019-08-07 19:52:29 -0400
committerDavid S. Miller <davem@davemloft.net>2019-08-09 13:03:30 -0700
commitc04b79b6cfd714144f6a2cf359603d82ee631e62 (patch)
tree3ef5597a3400666cfb0362c0ab1abbd666b87da3 /net/ipv4/tcp_timer.c
parentdevlink: remove pointless data_len arg from region snapshot create (diff)
downloadlinux-dev-c04b79b6cfd714144f6a2cf359603d82ee631e62.tar.xz
linux-dev-c04b79b6cfd714144f6a2cf359603d82ee631e62.zip
tcp: add new tcp_mtu_probe_floor sysctl
The current implementation of TCP MTU probing can considerably underestimate the MTU on lossy connections allowing the MSS to get down to 48. We have found that in almost all of these cases on our networks these paths can handle much larger MTUs meaning the connections are being artificially limited. Even though TCP MTU probing can raise the MSS back up we have seen this not to be the case causing connections to be "stuck" with an MSS of 48 when heavy loss is present. Prior to pushing out this change we could not keep TCP MTU probing enabled b/c of the above reasons. Now with a reasonble floor set we've had it enabled for the past 6 months. The new sysctl will still default to TCP_MIN_SND_MSS (48), but gives administrators the ability to control the floor of MSS probing. Signed-off-by: Josh Hunt <johunt@akamai.com> Signed-off-by: Eric Dumazet <edumazet@google.com> Acked-by: Neal Cardwell <ncardwell@google.com> Signed-off-by: David S. Miller <davem@davemloft.net>
Diffstat (limited to '')
-rw-r--r--net/ipv4/tcp_timer.c2
1 files changed, 1 insertions, 1 deletions
diff --git a/net/ipv4/tcp_timer.c b/net/ipv4/tcp_timer.c
index c801cd37cc2a..dbd9d2d0ee63 100644
--- a/net/ipv4/tcp_timer.c
+++ b/net/ipv4/tcp_timer.c
@@ -154,7 +154,7 @@ static void tcp_mtu_probing(struct inet_connection_sock *icsk, struct sock *sk)
} else {
mss = tcp_mtu_to_mss(sk, icsk->icsk_mtup.search_low) >> 1;
mss = min(net->ipv4.sysctl_tcp_base_mss, mss);
- mss = max(mss, 68 - tcp_sk(sk)->tcp_header_len);
+ mss = max(mss, net->ipv4.sysctl_tcp_mtu_probe_floor);
mss = max(mss, net->ipv4.sysctl_tcp_min_snd_mss);
icsk->icsk_mtup.search_low = tcp_mss_to_mtu(sk, mss);
}