This is a note to let you know that I've just added the patch titled tcp_bbr: cut pacing rate only if filled pipe to the 4.9-stable tree which can be found at: http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary The filename of the patch is: tcp_bbr-cut-pacing-rate-only-if-filled-pipe.patch and it can be found in the queue-4.9 subdirectory. If you, or anyone else, feels it should not be added to the stable tree, please let <stable@xxxxxxxxxxxxxxx> know about it. >From foo@baz Tue Aug 8 16:27:53 PDT 2017 From: Neal Cardwell <ncardwell@xxxxxxxxxx> Date: Fri, 14 Jul 2017 17:49:21 -0400 Subject: tcp_bbr: cut pacing rate only if filled pipe From: Neal Cardwell <ncardwell@xxxxxxxxxx> [ Upstream commit 4aea287e90dd61a48268ff2994b56f9799441b62 ] In bbr_set_pacing_rate(), which decides whether to cut the pacing rate, there was some code that considered exiting STARTUP to be equivalent to the notion of filling the pipe (i.e., bbr_full_bw_reached()). Specifically, as the code was structured, exiting STARTUP and going into PROBE_RTT could cause us to cut the pacing rate down to something silly and low, based on whatever bandwidth samples we've had so far, when it's possible that all of them have been small app-limited bandwidth samples that are not representative of the bandwidth available in the path. (The code was correct at the time it was written, but the state machine changed without this spot being adjusted correspondingly.) Fixes: 0f8782ea1497 ("tcp_bbr: add BBR congestion control") Signed-off-by: Neal Cardwell <ncardwell@xxxxxxxxxx> Signed-off-by: Yuchung Cheng <ycheng@xxxxxxxxxx> Signed-off-by: Soheil Hassas Yeganeh <soheil@xxxxxxxxxx> Signed-off-by: David S. Miller <davem@xxxxxxxxxxxxx> Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx> --- net/ipv4/tcp_bbr.c | 3 +-- 1 file changed, 1 insertion(+), 2 deletions(-) --- a/net/ipv4/tcp_bbr.c +++ b/net/ipv4/tcp_bbr.c @@ -191,12 +191,11 @@ static u64 bbr_rate_bytes_per_sec(struct */ static void bbr_set_pacing_rate(struct sock *sk, u32 bw, int gain) { - struct bbr *bbr = inet_csk_ca(sk); u64 rate = bw; rate = bbr_rate_bytes_per_sec(sk, rate, gain); rate = min_t(u64, rate, sk->sk_max_pacing_rate); - if (bbr->mode != BBR_STARTUP || rate > sk->sk_pacing_rate) + if (bbr_full_bw_reached(sk) || rate > sk->sk_pacing_rate) sk->sk_pacing_rate = rate; } Patches currently in stable-queue which might be from ncardwell@xxxxxxxxxx are queue-4.9/tcp_bbr-remove-sk_pacing_rate-0-transient-during-init.patch queue-4.9/tcp_bbr-introduce-bbr_bw_to_pacing_rate-helper.patch queue-4.9/tcp_bbr-introduce-bbr_init_pacing_rate_from_rtt-helper.patch queue-4.9/tcp_bbr-init-pacing-rate-on-first-rtt-sample.patch queue-4.9/tcp_bbr-cut-pacing-rate-only-if-filled-pipe.patch