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authorEric Dumazet <edumazet@google.com>2014-12-04 16:13:49 -0800
committerDavid S. Miller <davem@davemloft.net>2014-12-09 14:58:23 -0500
commit42eef7a0bb0989cd50d74e673422ff98a0ce4d7b (patch)
treea276db1a1c1ce97042450e9b1cb8cf8779861dd4 /net/ipv4/tcp_cubic.c
parent6e3a8a937c2f86ee0b2d354808fc026a143b4518 (diff)
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.c2
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);