[PATCH] tcp_cubic: enable TCP timestamps

[Lucas Nussbaum <lucas.nussbaum@loria.fr>]

The Hystart slow start algorithm requires precise RTT delay measurements
to decide when to leave slow start. However, currently, CUBIC doesn't
enable TCP timestamps. This can cause Hystart to mis-estimate the RTT,
and to leave slow start too early, generating bad performance since
convergence to the optimal cwnd is slower.

Timestamps are already used by TCP Illinois, LP, Vegas, Veno and Yeah.

Signed-off-by: Lucas Nussbaum <lucas.nussbaum@loria.fr>

-- 
| Lucas Nussbaum             MCF Université Nancy 2 |
| lucas.nussbaum@loria.fr         LORIA / AlGorille |
| http://www.loria.fr/~lnussbau/  +33 3 54 95 86 19 |

diff --git a/net/ipv4/tcp_cubic.c b/net/ipv4/tcp_cubic.c
index 71d5f2f..3a73509 100644
--- a/net/ipv4/tcp_cubic.c
+++ b/net/ipv4/tcp_cubic.c
@@ -406,6 +406,7 @@ static void bictcp_acked(struct sock *sk, u32 cnt, s32 rtt_us)
 }
 
 static struct tcp_congestion_ops cubictcp = {
+       .flags          = TCP_CONG_RTT_STAMP,
        .init           = bictcp_init,
        .ssthresh       = bictcp_recalc_ssthresh,
        .cong_avoid     = bictcp_cong_avoid,