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

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Date:	Fri, 5 Dec 2014 01:17:54 +0100
From:	Florian Westphal <fw@...len.de>
To:	Eric Dumazet <eric.dumazet@...il.com>
Cc:	David Miller <davem@...emloft.net>,
	netdev <netdev@...r.kernel.org>,
	Nandita Dukkipati <nanditad@...gle.com>,
	Neal Cardwell <ncardwell@...gle.com>,
	Yuchung Cheng <ycheng@...gle.com>,
	Sangtae Ha <sangtae.ha@...il.com>
Subject: Re: [PATCH net-next 1/2] tcp_cubic: add SNMP counters to track how
 effective is Hystart

Eric Dumazet <eric.dumazet@...il.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.
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