From 6fa338cbb044faed45fc4f932bce2ef6997a5245 Mon Sep 17 00:00:00 2001 From: =?utf8?q?Arkadiusz=20Mi=C5=9Bkiewicz?= Date: Sun, 27 Sep 2015 17:57:24 +0200 Subject: [PATCH] - cubic fix --- kernel-small_fixes.patch | 70 ++++++++++++++++++++++++++++++++++++++++ 1 file changed, 70 insertions(+) diff --git a/kernel-small_fixes.patch b/kernel-small_fixes.patch index d4b60349..fb7f26f7 100644 --- a/kernel-small_fixes.patch +++ b/kernel-small_fixes.patch @@ -26,3 +26,73 @@ exit fi done +From 30927520dbae297182990bb21d08762bcc35ce1d Mon Sep 17 00:00:00 2001 +From: Eric Dumazet +Date: Wed, 9 Sep 2015 21:55:07 -0700 +Subject: [PATCH] tcp_cubic: better follow cubic curve after idle period + +Jana Iyengar found an interesting issue on CUBIC : + +The epoch is only updated/reset initially and when experiencing losses. +The delta "t" of now - epoch_start can be arbitrary large after app idle +as well as the bic_target. Consequentially the slope (inverse of +ca->cnt) would be really large, and eventually ca->cnt would be +lower-bounded in the end to 2 to have delayed-ACK slow-start behavior. + +This particularly shows up when slow_start_after_idle is disabled +as a dangerous cwnd inflation (1.5 x RTT) after few seconds of idle +time. + +Jana initial fix was to reset epoch_start if app limited, +but Neal pointed out it would ask the CUBIC algorithm to recalculate the +curve so that we again start growing steeply upward from where cwnd is +now (as CUBIC does just after a loss). Ideally we'd want the cwnd growth +curve to be the same shape, just shifted later in time by the amount of +the idle period. + +Reported-by: Jana Iyengar +Signed-off-by: Eric Dumazet +Signed-off-by: Yuchung Cheng +Signed-off-by: Neal Cardwell +Cc: Stephen Hemminger +Cc: Sangtae Ha +Cc: Lawrence Brakmo +Signed-off-by: David S. Miller +--- + net/ipv4/tcp_cubic.c | 16 ++++++++++++++++ + 1 file changed, 16 insertions(+) + +diff --git a/net/ipv4/tcp_cubic.c b/net/ipv4/tcp_cubic.c +index 28011fb1..c6ded6b 100644 +--- a/net/ipv4/tcp_cubic.c ++++ b/net/ipv4/tcp_cubic.c +@@ -151,6 +151,21 @@ static void bictcp_init(struct sock *sk) + tcp_sk(sk)->snd_ssthresh = initial_ssthresh; + } + ++static void bictcp_cwnd_event(struct sock *sk, enum tcp_ca_event event) ++{ ++ if (event == CA_EVENT_TX_START) { ++ s32 delta = tcp_time_stamp - tcp_sk(sk)->lsndtime; ++ struct bictcp *ca = inet_csk_ca(sk); ++ ++ /* We were application limited (idle) for a while. ++ * Shift epoch_start to keep cwnd growth to cubic curve. ++ */ ++ if (ca->epoch_start && delta > 0) ++ ca->epoch_start += delta; ++ return; ++ } ++} ++ + /* calculate the cubic root of x using a table lookup followed by one + * Newton-Raphson iteration. + * Avg err ~= 0.195% +@@ -450,6 +465,7 @@ static struct tcp_congestion_ops cubictcp __read_mostly = { + .cong_avoid = bictcp_cong_avoid, + .set_state = bictcp_state, + .undo_cwnd = bictcp_undo_cwnd, ++ .cwnd_event = bictcp_cwnd_event, + .pkts_acked = bictcp_acked, + .owner = THIS_MODULE, + .name = "cubic", -- 2.44.0