| Message ID | 20180131204305.236274-1-ncardwell@google.com |
|---|---|
| State | Accepted, archived |
| Delegated to: | David Miller |
| Headers | show |
| Series | [net] tcp_bbr: fix pacing_gain to always be unity when using lt_bw | expand |
From: Neal Cardwell <ncardwell@google.com> Date: Wed, 31 Jan 2018 15:43:05 -0500 > This commit fixes the pacing_gain to remain at BBR_UNIT (1.0) when > using lt_bw and returning from the PROBE_RTT state to PROBE_BW. > > Previously, when using lt_bw, upon exiting PROBE_RTT and entering > PROBE_BW the bbr_reset_probe_bw_mode() code could sometimes randomly > end up with a cycle_idx of 0 and hence have bbr_advance_cycle_phase() > set a pacing gain above 1.0. In such cases this would result in a > pacing rate that is 1.25x higher than intended, potentially resulting > in a high loss rate for a little while until we stop using the lt_bw a > bit later. > > This commit is a stable candidate for kernels back as far as 4.9. > > Fixes: 0f8782ea1497 ("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> > Reported-by: Beyers Cronje <bcronje@gmail.com> Applied and queued up for -stable, thanks Neal.
diff --git a/net/ipv4/tcp_bbr.c b/net/ipv4/tcp_bbr.c index 8322f26e770e..25c5a0b60cfc 100644 --- a/net/ipv4/tcp_bbr.c +++ b/net/ipv4/tcp_bbr.c @@ -481,7 +481,8 @@ static void bbr_advance_cycle_phase(struct sock *sk) bbr->cycle_idx = (bbr->cycle_idx + 1) & (CYCLE_LEN - 1); bbr->cycle_mstamp = tp->delivered_mstamp; - bbr->pacing_gain = bbr_pacing_gain[bbr->cycle_idx]; + bbr->pacing_gain = bbr->lt_use_bw ? BBR_UNIT : + bbr_pacing_gain[bbr->cycle_idx]; } /* Gain cycling: cycle pacing gain to converge to fair share of available bw. */ @@ -490,8 +491,7 @@ static void bbr_update_cycle_phase(struct sock *sk, { struct bbr *bbr = inet_csk_ca(sk); - if ((bbr->mode == BBR_PROBE_BW) && !bbr->lt_use_bw && - bbr_is_next_cycle_phase(sk, rs)) + if (bbr->mode == BBR_PROBE_BW && bbr_is_next_cycle_phase(sk, rs)) bbr_advance_cycle_phase(sk); }
This commit fixes the pacing_gain to remain at BBR_UNIT (1.0) when using lt_bw and returning from the PROBE_RTT state to PROBE_BW. Previously, when using lt_bw, upon exiting PROBE_RTT and entering PROBE_BW the bbr_reset_probe_bw_mode() code could sometimes randomly end up with a cycle_idx of 0 and hence have bbr_advance_cycle_phase() set a pacing gain above 1.0. In such cases this would result in a pacing rate that is 1.25x higher than intended, potentially resulting in a high loss rate for a little while until we stop using the lt_bw a bit later. This commit is a stable candidate for kernels back as far as 4.9. Fixes: 0f8782ea1497 ("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> Reported-by: Beyers Cronje <bcronje@gmail.com> --- net/ipv4/tcp_bbr.c | 6 +++--- 1 file changed, 3 insertions(+), 3 deletions(-)