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Merge branch 'tcp_cubic-fix-spurious-HYSTART_DELAY-on-RTT-decrease'

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Neal Cardwell says:

====================
tcp_cubic: fix spurious HYSTART_DELAY on RTT decrease

This series fixes a long-standing bug in the TCP CUBIC
HYSTART_DELAY mechanim recently reported by Mirja Kuehlewind. The
code can cause a spurious exit of slow start in some particular
cases: upon an RTT decrease that happens on the 9th or later ACK
in a round trip. This series fixes the original Hystart code and
also the recent BPF implementation.
====================

Signed-off-by: David S. Miller <davem@davemloft.net>
This commit is contained in:
David S. Miller 2020-06-25 16:08:47 -07:00
commit 3b0e7dc0be
2 changed files with 4 additions and 6 deletions
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5
net/ipv4/tcp_cubic.c
View File

@ -432,10 +432,9 @@ static void hystart_update(struct sock *sk, u32 delay)
if (hystart_detect & HYSTART_DELAY) {
/* obtain the minimum delay of more than sampling packets */
if (ca->curr_rtt > delay)
ca->curr_rtt = delay;
if (ca->sample_cnt < HYSTART_MIN_SAMPLES) {
if (ca->curr_rtt > delay)
ca->curr_rtt = delay;
ca->sample_cnt++;
} else {
if (ca->curr_rtt > ca->delay_min +

5
tools/testing/selftests/bpf/progs/bpf_cubic.c
View File

@ -480,10 +480,9 @@ static __always_inline void hystart_update(struct sock *sk, __u32 delay)
if (hystart_detect & HYSTART_DELAY) {
/* obtain the minimum delay of more than sampling packets */
if (ca->curr_rtt > delay)
ca->curr_rtt = delay;
if (ca->sample_cnt < HYSTART_MIN_SAMPLES) {
if (ca->curr_rtt > delay)
ca->curr_rtt = delay;
ca->sample_cnt++;
} else {
if (ca->curr_rtt > ca->delay_min +