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

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Date:	Thu, 4 Dec 2014 19:55:45 -0500
From:	Neal Cardwell <ncardwell@...gle.com>
To:	Eric Dumazet <eric.dumazet@...il.com>
Cc:	David Miller <davem@...emloft.net>,
	netdev <netdev@...r.kernel.org>,
	Nandita Dukkipati <nanditad@...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

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

Acked-by: Neal Cardwell <ncardwell@...gle.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
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