linux-kernel - Re: TCP reaching to maximum throughput after a long time

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Message-ID: <1460492253.6473.596.camel@edumazet-glaptop3.roam.corp.google.com>
Date:	Tue, 12 Apr 2016 13:17:33 -0700
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Ben Greear <greearb@...delatech.com>
Cc:	"Machani, Yaniv" <yanivma@...com>, netdev <netdev@...r.kernel.org>,
	"David S. Miller" <davem@...emloft.net>,
	Eric Dumazet <edumazet@...gle.com>,
	Neal Cardwell <ncardwell@...gle.com>,
	Yuchung Cheng <ycheng@...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 Tue, 2016-04-12 at 13:11 -0700, Ben Greear wrote:
> On 04/12/2016 12:31 PM, Machani, Yaniv wrote:
> > On Tue, Apr 12, 2016 at 18:04:52, Ben Greear wrote:
> >> On 04/12/2016 07:52 AM, Eric Dumazet wrote:
> >>> On Tue, 2016-04-12 at 12:17 +0000, Machani, Yaniv wrote:
> >>>>
> >>
> >> If you are using 'Cubic' TCP congestion control, then please try
> >> something different.
> >> It was broken last I checked, at least when used with the ath10k driver.
> >>
> >
> > Thanks Ben, this indeed seems to be the issue !
> > Switching to reno got me to max throughput instantly.
> >
> > I'm still looking through the thread you have shared, but from what I understand there is no planned fix for it ?
> 
> I think at the time it was blamed on ath10k and no one cared to try to fix it.
> 
> Or, maybe no one really uses CUBIC anymore?
> 
> Either way, I have no plans to try to fix CUBIC, but maybe someone who knows
> this code better could give it a try.

Well, cubic seems to work in many cases, assuming they are not too many
drops.

Assuming one flow can get nominal speed in few RTT is kind a dream, and
so far nobody claimed a CC was able to do that, while still being fair
and resilient.

TCP CC are full of heuristics, and by definition heuristics that were
working 6 years ago might need to be refreshed.

We are still maintaining Cubic for sure.