mirror of
https://git.kernel.org/pub/scm/linux/kernel/git/next/linux-next.git
synced 2025-01-10 07:50:04 +00:00
tcp_cubic: fix spurious Hystart ACK train detections for not-cwnd-limited flows
While testing BIG TCP patch series, I was expecting that TCP_RR workloads with 80KB requests/answers would send one 80KB TSO packet, then being received as a single GRO packet. It turns out this was not happening, and the root cause was that cubic Hystart ACK train was triggering after a few (2 or 3) rounds of RPC. Hystart was wrongly setting CWND/SSTHRESH to 30, while my RPC needed a budget of ~20 segments. Ideally these TCP_RR flows should not exit slow start. Cubic Hystart should reset itself at each round, instead of assuming every TCP flow is a bulk one. Note that even after this patch, Hystart can still trigger, depending on scheduling artifacts, but at a higher CWND/SSTHRESH threshold, keeping optimal TSO packet sizes. Tested: ip link set dev eth0 gro_ipv6_max_size 131072 gso_ipv6_max_size 131072 nstat -n; netperf -H ... -t TCP_RR -l 5 -- -r 80000,80000 -K cubic; nstat|egrep "Ip6InReceives|Hystart|Ip6OutRequests" Before: 8605 Ip6InReceives 87541 0.0 Ip6OutRequests 129496 0.0 TcpExtTCPHystartTrainDetect 1 0.0 TcpExtTCPHystartTrainCwnd 30 0.0 After: 8760 Ip6InReceives 88514 0.0 Ip6OutRequests 87975 0.0 Fixes: ae27e98a5152 ("[TCP] CUBIC v2.3") Co-developed-by: Neal Cardwell <ncardwell@google.com> Signed-off-by: Neal Cardwell <ncardwell@google.com> Signed-off-by: Eric Dumazet <edumazet@google.com> Cc: Stephen Hemminger <stephen@networkplumber.org> Cc: Yuchung Cheng <ycheng@google.com> Cc: Soheil Hassas Yeganeh <soheil@google.com> Link: https://lore.kernel.org/r/20211123202535.1843771-1-eric.dumazet@gmail.com Signed-off-by: Jakub Kicinski <kuba@kernel.org>
This commit is contained in:
parent
550b8e1d18
commit
4e1fddc98d
@ -330,8 +330,6 @@ static void cubictcp_cong_avoid(struct sock *sk, u32 ack, u32 acked)
|
||||
return;
|
||||
|
||||
if (tcp_in_slow_start(tp)) {
|
||||
if (hystart && after(ack, ca->end_seq))
|
||||
bictcp_hystart_reset(sk);
|
||||
acked = tcp_slow_start(tp, acked);
|
||||
if (!acked)
|
||||
return;
|
||||
@ -391,6 +389,9 @@ static void hystart_update(struct sock *sk, u32 delay)
|
||||
struct bictcp *ca = inet_csk_ca(sk);
|
||||
u32 threshold;
|
||||
|
||||
if (after(tp->snd_una, ca->end_seq))
|
||||
bictcp_hystart_reset(sk);
|
||||
|
||||
if (hystart_detect & HYSTART_ACK_TRAIN) {
|
||||
u32 now = bictcp_clock_us(sk);
|
||||
|
||||
|
Loading…
x
Reference in New Issue
Block a user