netdev - Re: tcp wifi upload performance and lots of ACKs

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Message-ID: <CAEnQRZCNUYmP88Ocm_nG7gpA1Qcwy1tOc6kgCgZ7RqXcxQsHhg@mail.gmail.com>
Date:	Mon, 4 Jun 2012 22:22:01 +0300
From:	Daniel Baluta <dbaluta@...acom.com>
To:	Ben Greear <greearb@...delatech.com>
Cc:	netdev <netdev@...r.kernel.org>
Subject: Re: tcp wifi upload performance and lots of ACKs

On Mon, Jun 4, 2012 at 9:29 PM, Ben Greear <greearb@...delatech.com> wrote:
> I'm going some TCP performance testing on wifi -> LAN interface connections.
>  With
> UDP, we can get around 250Mbps of payload throughput.  With TCP, max is
> about 80Mbps.
>
> I think the problem is that there are way too many ACK packets, and
> bi-directional
> traffic on wifi interfaces really slows things down.  (About 7000 pkts per
> second in
> upload direction, 2000 pps download.  And the vast majority of the download
> pkts
> are 66 byte ACK pkts from what I can tell.)
>
> Kernel is 3.3.7+
>
> Anyone know of any tuning parameters that would let the receiving socket
> wait a
> bit longer and send more ACK data in fewer packets?

An ACK is generated after every second full sized segment or a timeout
expires.

Currently, there is no way to tune these parameters. Here is an experimental
patch [1]. If anyone, thinks that this patch has a chance to get accepted
I will be happily try to further improve it.

>
> Packet traces and other info available if anyone wants to take a look.

thanks,
Daniel.

[1] http://marc.info/?l=linux-netdev&m=131983649130350&w=2
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