Re: tcp wifi upload performance and lots of ACKs

[Ben Greear <greearb@xxxxxxxxxxxxxxx>]

On 06/04/2012 12:32 PM, Eric Dumazet wrote:
> On Mon, 2012-06-04 at 11:29 -0700, Ben Greear 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?
>
> Well, thats half duplex days...

WiFi is still half-duplex, and isn't changing any time soon I think.

> There is the ACK every 2 packets rule of thumb, so that tcp sender can
> increase its cwnd.
>
> Then, some folks tried submitting patches to make '2' more like 10 or
> 15, but this went nowhere.
>
> Other idea is to arm a timer and defer ACK sending, in the hope we
> receive another packet very soon.

From a quick read of Daniel's patch..it seems there is already a
timer that could be used for this?

> That could be done with a special qdisc, sort of netem...

That sounds like a horrible hack :)

Ben

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

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