netdev - Re: [Patch net-next] tcp: add a global sysctl to control TCP delayed ack

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Date:	Thu, 04 Apr 2013 16:39:04 -0700
From:	Ben Greear <greearb@...delatech.com>
To:	David Miller <davem@...emloft.net>
CC:	hannes@...essinduktion.org, amwang@...hat.com,
	netdev@...r.kernel.org, eric.dumazet@...il.com, rick.jones2@...com,
	shemminger@...tta.com, tgraf@...g.ch, David.Laight@...LAB.COM
Subject: Re: [Patch net-next] tcp: add a global sysctl to control TCP delayed
 ack

On 04/04/2013 04:25 PM, David Miller wrote:
> From: Hannes Frederic Sowa <hannes@...essinduktion.org>
> Date: Fri, 5 Apr 2013 00:48:10 +0200
>
>> I totally understand the objections that were given regarding this
>> patch. But for defense of this patch we also provide a knob to disable
>> slow start after idle, which from my point of view is as "evil" as
>> this change.
>
> I completely disagree, slow start after idle is way too aggressively
> throwing past history away, so turning that off is much safer.

I've been carrying a per-socket way to control delayed ack in my tree for a while,
and it is a big performance gain on wifi networks where the network is
basically half-duplex.  If I recall correctly, it's worth 50+Mbps
throughput improvement in some cases.  If it matters, I can post more
detailed numbers.

There are drawbacks when you set delayed ack too high:  The ramp-up time
for TCP takes a good bit longer.  But, some applications may want to trade
slower startup time for better bulk transport, and at moderate delayed-ack
values, the ramp up time is not noticeably impaired.

Thanks,
Ben

-- 
Ben Greear <greearb@...delatech.com>
Candela Technologies Inc  http://www.candelatech.com

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