[PATCH net-next 1/2] tcp_cubic: add SNMP counters to track how effective is Hystart

[PATCH net-next 1/2] tcp_cubic: add SNMP counters to track how effective is Hystart

[Eric Dumazet]

From: Eric Dumazet <edumazet@google.com>

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>
---
 include/uapi/linux/snmp.h |    4 ++++
 net/ipv4/proc.c           |    4 ++++
 net/ipv4/tcp_cubic.c      |   31 ++++++++++++++++++++++---------
 3 files changed, 30 insertions(+), 9 deletions(-)

diff --git a/include/uapi/linux/snmp.h b/include/uapi/linux/snmp.h
index 30f541b32895..b22224100011 100644
--- a/include/uapi/linux/snmp.h
+++ b/include/uapi/linux/snmp.h
@@ -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
 };
 
diff --git a/net/ipv4/proc.c b/net/ipv4/proc.c
index 6513ade8d6dc..8f9cd200ce20 100644
--- a/net/ipv4/proc.c
+++ b/net/ipv4/proc.c
@@ -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
 };
 
diff --git a/net/ipv4/tcp_cubic.c b/net/ipv4/tcp_cubic.c
index 20de0118c98e..c1d07c7ed03d 100644
--- a/net/ipv4/tcp_cubic.c
+++ b/net/ipv4/tcp_cubic.c
@@ -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;
 	}
 }
 

Re: [PATCH net-next 1/2] tcp_cubic: add SNMP counters to track how effective is Hystart

[Florian Westphal]

Eric Dumazet <eric.dumazet@gmail.com> wrote:
> 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

Alternatively we could add INET_DIAG_CUBICINFO and export such info via ss
tool.

Re: [PATCH net-next 1/2] tcp_cubic: add SNMP counters to track how effective is Hystart

[Eric Dumazet]

On Fri, 2014-12-05 at 01:17 +0100, Florian Westphal wrote:

> Alternatively we could add INET_DIAG_CUBICINFO and export such info via ss
> tool.

Thats a complete different model.

When studying some param changes on servers handling million of flows,
SNMP hosts stats are giving the picture, without having to collect huge
ss info in the background and aggregating it.

Re: [PATCH net-next 1/2] tcp_cubic: add SNMP counters to track how effective is Hystart

[Neal Cardwell]

On Thu, Dec 4, 2014 at 7:13 PM, Eric Dumazet <eric.dumazet@gmail.com> wrote:
> From: Eric Dumazet <edumazet@google.com>
>
> 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>

Very nice. IMHO it's great to have these as SNMP counters, so we don't
need special tools to get aggregate stats for all connections.

neal

Re: [PATCH net-next 1/2] tcp_cubic: add SNMP counters to track how effective is Hystart

[David Miller]

From: Eric Dumazet <eric.dumazet@gmail.com>
Date: Thu, 04 Dec 2014 16:13:23 -0800

> From: Eric Dumazet <edumazet@google.com>
> 
> 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>

Applied.