netdev - RE: TCP reaching to maximum throughput after a long time

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Date:	Wed, 13 Apr 2016 20:26:32 +0000
From:	"Machani, Yaniv" <yanivma@...com>
To:	Neal Cardwell <ncardwell@...gle.com>,
	Eric Dumazet <eric.dumazet@...il.com>
CC:	Yuchung Cheng <ycheng@...gle.com>,
	Ben Greear <greearb@...delatech.com>,
	netdev <netdev@...r.kernel.org>,
	"David S. Miller" <davem@...emloft.net>,
	Eric Dumazet <edumazet@...gle.com>,
	Nandita Dukkipati <nanditad@...gle.com>,
	open list <linux-kernel@...r.kernel.org>,
	"Kama, Meirav" <meiravk@...com>
Subject: RE: TCP reaching to maximum throughput after a long time

On Wed, Apr 13, 2016 at 17:32:29, Neal Cardwell wrote:
> Miller; Eric Dumazet; Nandita Dukkipati; open list; Kama, Meirav
> Subject: Re: TCP reaching to maximum throughput after a long time
> 
> I like the idea to disable hystart ack-train.
> 
> 
> Yaniv, can you please re-run your test with CUBIC in three different
> scenarios:
> 
> a) echo 0 > /sys/module/tcp_cubic/parameters/hystart_detect
This fixes the issues, got to max throughput immediately. 

> 
> b) echo 1 > /sys/module/tcp_cubic/parameters/hystart_detect
> 
This shows the same results as before, starting low and increasing slowly.

>
> c) echo 2 > /sys/module/tcp_cubic/parameters/hystart_detect
This gets us a bit higher at the beginning, but never (waited ~60 sec) goes to the max.


Appreciate your help on this.
Yaniv
> 
> 
> This should help us isolate whether the hystart ack-train algorithm is 
> causing problems in this particular case.
> 
> Thanks!
> neal
> 
> 
> 
> On Tue, Apr 12, 2016 at 11:32 PM, Eric Dumazet 
> <eric.dumazet@...il.com>
> wrote:
> 
> 
> 	On Tue, 2016-04-12 at 20:08 -0700, Yuchung Cheng wrote:
> 
> 	> based on the prev thread I propose we disable hystart ack-train. It 
> is
> 	> brittle under various circumstances. We've disabled that at Google 
> for
> 	> years.
> 
> 	Right, but because we also use sch_fq packet scheduler and pacing ;)
> 
> 
> 
>