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tcp: make congestion control optionally skip slow start after idle 

Congestion control modules that want full control over congestion
control behavior do not want the cwnd modifications controlled by
the sysctl_tcp_slow_start_after_idle code path.
So skip those code paths for CC modules that use the cong_control()
API.
As an example, those cwnd effects are not desired for the BBR congestion
control algorithm.

Fixes: c0402760f5 ("tcp: new CC hook to set sending rate with rate_sample in any CA state")
Signed-off-by: Wei Wang <weiwan@google.com>
Signed-off-by: Yuchung Cheng <ycheng@google.com>
Signed-off-by: Neal Cardwell <ncardwell@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
This commit is contained in:
Wei Wang 2017-05-05 12:53:23 -07:00 committed by David S. Miller
parent 82486aa6f1
commit 1b1fc3fdda
2 changed files with 6 additions and 2 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

4
include/net/tcp.h
View File

@ -1234,10 +1234,12 @@ void tcp_cwnd_restart(struct sock *sk, s32 delta);
static inline void tcp_slow_start_after_idle_check(struct sock *sk)
{
const struct tcp_congestion_ops *ca_ops = inet_csk(sk)->icsk_ca_ops;
struct tcp_sock *tp = tcp_sk(sk);
s32 delta;
if (!sysctl_tcp_slow_start_after_idle || tp->packets_out)
if (!sysctl_tcp_slow_start_after_idle || tp->packets_out ||
ca_ops->cong_control)
return;
delta = tcp_time_stamp - tp->lsndtime;
if (delta > inet_csk(sk)->icsk_rto)

4
net/ipv4/tcp_output.c
View File

@ -1514,6 +1514,7 @@ static void tcp_cwnd_application_limited(struct sock *sk)
static void tcp_cwnd_validate(struct sock *sk, bool is_cwnd_limited)
{
const struct tcp_congestion_ops *ca_ops = inet_csk(sk)->icsk_ca_ops;
struct tcp_sock *tp = tcp_sk(sk);
/* Track the maximum number of outstanding packets in each
@ -1536,7 +1537,8 @@ static void tcp_cwnd_validate(struct sock *sk, bool is_cwnd_limited)
tp->snd_cwnd_used = tp->packets_out;
if (sysctl_tcp_slow_start_after_idle &&
(s32)(tcp_time_stamp - tp->snd_cwnd_stamp) >= inet_csk(sk)->icsk_rto)
(s32)(tcp_time_stamp - tp->snd_cwnd_stamp) >= inet_csk(sk)->icsk_rto &&
!ca_ops->cong_control)
tcp_cwnd_application_limited(sk);
/* The following conditions together indicate the starvation