tcp_cubic: refine Hystart delay threshold
In commit 2b4636a5f8
("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>
This commit is contained in:
parent
6e3a8a937c
commit
42eef7a0bb
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@ -393,7 +393,7 @@ static void hystart_update(struct sock *sk, u32 delay)
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ca->sample_cnt++;
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} else {
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if (ca->curr_rtt > ca->delay_min +
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HYSTART_DELAY_THRESH(ca->delay_min>>4)) {
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HYSTART_DELAY_THRESH(ca->delay_min >> 3)) {
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ca->found |= HYSTART_DELAY;
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NET_INC_STATS_BH(sock_net(sk),
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LINUX_MIB_TCPHYSTARTDELAYDETECT);
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