This is a note to let you know that I've just added the patch titled
tcp_bbr: fix pacing_gain to always be unity when using lt_bw
to the 4.15-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-fix-pacing_gain-to-always-be-unity-when-using-lt_bw.patch
and it can be found in the queue-4.15 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 Wed Feb 7 11:29:33 PST 2018
From: Neal Cardwell <ncardwell@xxxxxxxxxx>
Date: Wed, 31 Jan 2018 15:43:05 -0500
Subject: tcp_bbr: fix pacing_gain to always be unity when using lt_bw
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
@@ -481,7 +481,8 @@ 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. */
@@ -490,8 +491,7 @@ 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);
}
Patches currently in stable-queue which might be from ncardwell@xxxxxxxxxx are
queue-4.15/tcp_bbr-fix-pacing_gain-to-always-be-unity-when-using-lt_bw.patch