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authorNeal Cardwell <ncardwell@google.com>2018-01-31 15:43:05 -0500
committerDavid S. Miller <davem@davemloft.net>2018-02-01 09:43:38 -0500
commit3aff3b4b986e51bcf4ab249e5d48d39596e0df6a (patch)
tree578224f45d5d80e61ccfd2fa008bc65145b16c8e
parent2e85283dabc22f4715b136e8a7426bd9bef4ce69 (diff)
downloadlinux-3aff3b4b986e51bcf4ab249e5d48d39596e0df6a.tar.bz2
tcp_bbr: fix pacing_gain to always be unity when using lt_bw
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> Signed-off-by: David S. Miller <davem@davemloft.net>
-rw-r--r--net/ipv4/tcp_bbr.c6
1 files changed, 3 insertions, 3 deletions
diff --git a/net/ipv4/tcp_bbr.c b/net/ipv4/tcp_bbr.c
index 785712be5b0d..a471f696e13c 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);
}