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| author | Eric Dumazet <edumazet@google.com> | 2014-12-04 16:13:49 -0800 |
|---|---|---|
| committer | David S. Miller <davem@davemloft.net> | 2014-12-09 14:58:23 -0500 |
| commit | 42eef7a0bb0989cd50d74e673422ff98a0ce4d7b (patch) | |
| tree | a276db1a1c1ce97042450e9b1cb8cf8779861dd4 /net/ipv4/tcp_cubic.c | |
| parent | 6e3a8a937c2f86ee0b2d354808fc026a143b4518 (diff) | |
| download | lwn-42eef7a0bb0989cd50d74e673422ff98a0ce4d7b.tar.gz lwn-42eef7a0bb0989cd50d74e673422ff98a0ce4d7b.zip | |
tcp_cubic: refine Hystart delay threshold
In commit 2b4636a5f8ca ("tcp_cubic: make the delay threshold of HyStart
less sensitive"), HYSTART_DELAY_MIN was changed to 4 ms.
The remaining problem is that using delay_min + (delay_min/16) as the
threshold is too sensitive.
6.25 % of variation is too small for rtt above 60 ms, which are not
uncommon.
Lets use 12.5 % instead (delay_min + (delay_min/8))
Tested:
80 ms RTT between peers, FQ/pacing packet scheduler on sender.
10 bulk transfers of 10 seconds :
nstat >/dev/null
for i in `seq 1 10`
do
netperf -H remote -- -k THROUGHPUT | grep THROUGHPUT
done
nstat | grep Hystart
With the 6.25 % threshold :
THROUGHPUT=20.66
THROUGHPUT=249.38
THROUGHPUT=254.10
THROUGHPUT=14.94
THROUGHPUT=251.92
THROUGHPUT=237.73
THROUGHPUT=19.18
THROUGHPUT=252.89
THROUGHPUT=21.32
THROUGHPUT=15.58
TcpExtTCPHystartTrainDetect 2 0.0
TcpExtTCPHystartTrainCwnd 4756 0.0
TcpExtTCPHystartDelayDetect 5 0.0
TcpExtTCPHystartDelayCwnd 180 0.0
With the 12.5 % threshold
THROUGHPUT=251.09
THROUGHPUT=247.46
THROUGHPUT=250.92
THROUGHPUT=248.91
THROUGHPUT=250.88
THROUGHPUT=249.84
THROUGHPUT=250.51
THROUGHPUT=254.15
THROUGHPUT=250.62
THROUGHPUT=250.89
TcpExtTCPHystartTrainDetect 1 0.0
TcpExtTCPHystartTrainCwnd 3175 0.0
Signed-off-by: Eric Dumazet <edumazet@google.com>
Acked-by: Neal Cardwell <ncardwell@google.com>
Tested-by: Neal Cardwell <ncardwell@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Diffstat (limited to 'net/ipv4/tcp_cubic.c')
| -rw-r--r-- | net/ipv4/tcp_cubic.c | 2 |
1 files changed, 1 insertions, 1 deletions
diff --git a/net/ipv4/tcp_cubic.c b/net/ipv4/tcp_cubic.c index c1d07c7ed03d..6b6002416a73 100644 --- a/net/ipv4/tcp_cubic.c +++ b/net/ipv4/tcp_cubic.c @@ -393,7 +393,7 @@ static void hystart_update(struct sock *sk, u32 delay) ca->sample_cnt++; } else { if (ca->curr_rtt > ca->delay_min + - HYSTART_DELAY_THRESH(ca->delay_min>>4)) { + HYSTART_DELAY_THRESH(ca->delay_min >> 3)) { ca->found |= HYSTART_DELAY; NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_TCPHYSTARTDELAYDETECT); |