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tcp_cubic: add SNMP counters to track how effective is Hystart

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When deploying FQ pacing, one thing we noticed is that CUBIC Hystart
triggers too soon.

Having SNMP counters to have an idea of how often the various Hystart
methods trigger is useful prior to any modifications.

This patch adds SNMP counters tracking, how many time "ack train" or
"Delay" based Hystart triggers, and cumulative sum of cwnd at the time
Hystart decided to end SS (Slow Start)

myhost:~# nstat -a | grep Hystart
TcpExtTCPHystartTrainDetect     9                  0.0
TcpExtTCPHystartTrainCwnd       20650              0.0
TcpExtTCPHystartDelayDetect     10                 0.0
TcpExtTCPHystartDelayCwnd       360                0.0

->
 Train detection was triggered 9 times, and average cwnd was
 20650/9=2294,
 Delay detection was triggered 10 times and average cwnd was 36

Signed-off-by: Eric Dumazet <edumazet@google.com>
Acked-by: Neal Cardwell <ncardwell@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
This commit is contained in:
Eric Dumazet 2014-12-04 16:13:23 -08:00 committed by David S. Miller
parent 5cccc702fd
commit 6e3a8a937c
3 changed files with 30 additions and 9 deletions
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4
include/uapi/linux/snmp.h
View file

@ -266,6 +266,10 @@ enum
LINUX_MIB_TCPWANTZEROWINDOWADV, /* TCPWantZeroWindowAdv */
LINUX_MIB_TCPSYNRETRANS, /* TCPSynRetrans */
LINUX_MIB_TCPORIGDATASENT, /* TCPOrigDataSent */
LINUX_MIB_TCPHYSTARTTRAINDETECT, /* TCPHystartTrainDetect */
LINUX_MIB_TCPHYSTARTTRAINCWND, /* TCPHystartTrainCwnd */
LINUX_MIB_TCPHYSTARTDELAYDETECT, /* TCPHystartDelayDetect */
LINUX_MIB_TCPHYSTARTDELAYCWND, /* TCPHystartDelayCwnd */
__LINUX_MIB_MAX
};

4
net/ipv4/proc.c
View file

@ -288,6 +288,10 @@ static const struct snmp_mib snmp4_net_list[] = {
SNMP_MIB_ITEM("TCPWantZeroWindowAdv", LINUX_MIB_TCPWANTZEROWINDOWADV),
SNMP_MIB_ITEM("TCPSynRetrans", LINUX_MIB_TCPSYNRETRANS),
SNMP_MIB_ITEM("TCPOrigDataSent", LINUX_MIB_TCPORIGDATASENT),
SNMP_MIB_ITEM("TCPHystartTrainDetect", LINUX_MIB_TCPHYSTARTTRAINDETECT),
SNMP_MIB_ITEM("TCPHystartTrainCwnd", LINUX_MIB_TCPHYSTARTTRAINCWND),
SNMP_MIB_ITEM("TCPHystartDelayDetect", LINUX_MIB_TCPHYSTARTDELAYDETECT),
SNMP_MIB_ITEM("TCPHystartDelayCwnd", LINUX_MIB_TCPHYSTARTDELAYCWND),
SNMP_MIB_SENTINEL
};

31
net/ipv4/tcp_cubic.c
View file

@ -363,16 +363,28 @@ static void hystart_update(struct sock *sk, u32 delay)
struct tcp_sock *tp = tcp_sk(sk);
struct bictcp *ca = inet_csk_ca(sk);
if (!(ca->found & hystart_detect)) {
if (ca->found & hystart_detect)
return;
if (hystart_detect & HYSTART_ACK_TRAIN) {
u32 now = bictcp_clock();
/* first detection parameter - ack-train detection */
if ((s32)(now - ca->last_ack) <= hystart_ack_delta) {
ca->last_ack = now;
if ((s32)(now - ca->round_start) > ca->delay_min >> 4)
if ((s32)(now - ca->round_start) > ca->delay_min >> 4) {
ca->found |= HYSTART_ACK_TRAIN;
NET_INC_STATS_BH(sock_net(sk),
LINUX_MIB_TCPHYSTARTTRAINDETECT);
NET_ADD_STATS_BH(sock_net(sk),
LINUX_MIB_TCPHYSTARTTRAINCWND,
tp->snd_cwnd);
tp->snd_ssthresh = tp->snd_cwnd;
}
}
}
if (hystart_detect & HYSTART_DELAY) {
/* obtain the minimum delay of more than sampling packets */
if (ca->sample_cnt < HYSTART_MIN_SAMPLES) {
if (ca->curr_rtt == 0 || ca->curr_rtt > delay)
@ -381,15 +393,16 @@ 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>>4)) {
ca->found |= HYSTART_DELAY;
NET_INC_STATS_BH(sock_net(sk),
LINUX_MIB_TCPHYSTARTDELAYDETECT);
NET_ADD_STATS_BH(sock_net(sk),
LINUX_MIB_TCPHYSTARTDELAYCWND,
tp->snd_cwnd);
tp->snd_ssthresh = tp->snd_cwnd;
}
}
/*
* Either one of two conditions are met,
* we exit from slow start immediately.
*/
if (ca->found & hystart_detect)
tp->snd_ssthresh = tp->snd_cwnd;
}
}