4.9-stable review patch. If anyone has any objections, please let me know.
------------------
From: Neal Cardwell <ncardwell@xxxxxxxxxx>
[ Upstream commit 3aff3b4b986e51bcf4ab249e5d48d39596e0df6a ]
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@xxxxxxxxxx>
Signed-off-by: Yuchung Cheng <ycheng@xxxxxxxxxx>
Signed-off-by: Soheil Hassas Yeganeh <soheil@xxxxxxxxxx>
Reported-by: Beyers Cronje <bcronje@xxxxxxxxx>
Signed-off-by: David S. Miller <davem@xxxxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
net/ipv4/tcp_bbr.c | 6 +++---
1 file changed, 3 insertions(+), 3 deletions(-)
--- a/net/ipv4/tcp_bbr.c
+++ b/net/ipv4/tcp_bbr.c
@@ -452,7 +452,8 @@ static void bbr_advance_cycle_phase(stru
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. */
@@ -461,8 +462,7 @@ static void bbr_update_cycle_phase(struc
{
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);
}