linux-kernel - Re: [PATCH] net: tcp: Fix a PTO timing granularity issue

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Date:	Tue, 26 May 2015 11:25:21 -0700
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Ido Yariv <ido@...ery.com>
Cc:	"David S. Miller" <davem@...emloft.net>,
	Alexey Kuznetsov <kuznet@....inr.ac.ru>,
	James Morris <jmorris@...ei.org>,
	Hideaki YOSHIFUJI <yoshfuji@...ux-ipv6.org>,
	Patrick McHardy <kaber@...sh.net>,
	Nandita Dukkipati <nanditad@...gle.com>,
	netdev@...r.kernel.org, linux-kernel@...r.kernel.org,
	Ido Yariv <idox.yariv@...el.com>
Subject: Re: [PATCH] net: tcp: Fix a PTO timing granularity issue

On Tue, 2015-05-26 at 13:55 -0400, Ido Yariv wrote:

> 
> The platform this was tested on was an embedded platform with a wifi
> module (11n, 20MHZ). The other end was a computer running Windows, and
> the benchmarking software was IxChariot.
> The whole setup was running in a shielded box with minimal
> interferences.
> 
> As it seems, the throughput was limited by the congestion window.
> Further analysis led to TLP - the fact that its timer was expiring
> prematurely impacted cwnd, which in turn prevented the wireless driver
> from having enough skbs to buffer and send.
> 
> Increasing the size of the chunks being sent had a similar impact on
> throughput, presumably because the congestion window had enough time to
> increase.
> 
> Changing the congestion window to Westwood from cubic/reno also had a
> similar impact on throughput.
> 

Have you tested what results you had by completely disabling TLP ?

Maybe a timer of 10 to 20ms is too short anyway in your testbed.



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