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tcp_bbr: fix to zero idle_restart only upon S/ACKed data

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Previously the bbr->idle_restart tracking was zeroing out the
bbr->idle_restart bit upon ACKs that did not SACK or ACK anything,
e.g. receiving incoming data or receiver window updates. In such
situations BBR would forget that this was a restart-from-idle
situation, and if the min_rtt had expired it would unnecessarily enter
PROBE_RTT (even though we were actually restarting from idle but had
merely forgotten that fact).

The fix is simple: we need to remember we are restarting from idle
until we receive a S/ACK for some data (a S/ACK for the first flight
of data we send as we are restarting).

This commit is a stable candidate for kernels back as far as 4.9.

Fixes: 0f8782ea14 ("tcp_bbr: add BBR congestion control")
Signed-off-by: Neal Cardwell <ncardwell@google.com>
Signed-off-by: Yuchung Cheng <ycheng@google.com>
Signed-off-by: Soheil Hassas Yeganeh <soheil@google.com>
Signed-off-by: Priyaranjan Jha <priyarjha@google.com>
Signed-off-by: Yousuk Seung <ysseung@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
This commit is contained in:
Neal Cardwell 2018-05-01 21:45:41 -04:00 committed by David S. Miller
parent 5e5add172e
commit e6e6a278b1
1 changed files with 3 additions and 1 deletions
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4
net/ipv4/tcp_bbr.c
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@ -806,7 +806,9 @@ static void bbr_update_min_rtt(struct sock *sk, const struct rate_sample *rs)
}
}
}
bbr->idle_restart = 0;
/* Restart after idle ends only once we process a new S/ACK for data */
if (rs->delivered > 0)
bbr->idle_restart = 0;
}
static void bbr_update_model(struct sock *sk, const struct rate_sample *rs)