* [Bloat] Fwd: [PATCH net-next 2/2] tcp_cubic: refine Hystart delay threshold
[not found] <1417738429.22424.29.camel@edumazet-glaptop2.roam.corp.google.com>
@ 2014-12-05 1:11 ` Dave Taht
0 siblings, 0 replies; only message in thread
From: Dave Taht @ 2014-12-05 1:11 UTC (permalink / raw)
To: bloat, aqm
fixing hystart at longer rtts with fq + pacing...
---------- Forwarded message ----------
From: Eric Dumazet <eric.dumazet@gmail.com>
Date: Thu, Dec 4, 2014 at 4:13 PM
Subject: [PATCH net-next 2/2] tcp_cubic: refine Hystart delay threshold
To: David Miller <davem@davemloft.net>
Cc: netdev <netdev@vger.kernel.org>, Nandita Dukkipati
<nanditad@google.com>, Neal Cardwell <ncardwell@google.com>, Yuchung
Cheng <ycheng@google.com>, Sangtae Ha <sangtae.ha@gmail.com>
From: Eric Dumazet <edumazet@google.com>
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>
---
net/ipv4/tcp_cubic.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/net/ipv4/tcp_cubic.c b/net/ipv4/tcp_cubic.c
index c1d07c7ed03d7d37fa28d1509093e686f78134d2..6b6002416a73950d493661ea1459870f49917efc
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);
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--
Dave Täht
thttp://www.bufferbloat.net/projects/bloat/wiki/Upcoming_Talks
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