[OpenAFS] Re: WAN speed

[Simon Wilkinson]

On 22 Mar 2012, at 15:09, Andrew Deason wrote:

> On Thu, 22 Mar 2012 10:18:44 -0400
> chas williams - CONTRACTOR <chas@cmf.nrl.navy.mil> wrote:
>=20
>> but besides this limit, there is also another determining factor in
>> rx.  rx, like tcp, negotiates a window of data to send before waiting
>> for an ack from the other side which lets me data get sent.  if the
>> window doesnt grow large enough, then you will not be able to get the
>> full bandwidth of the link.  i believe usually, you hit the window
>> size limit in rx before anything else though.
>>=20
>> there are some problems with using larger window sizes in rx related
>> to queue management efficiency as i recall.
>=20
> But even without that, the window size still has a limit much smaller
> than TCP.

That limit is imposed because it is the point at which the current RX =
implementation loses the queue efficiency/throughput tradeoff. You can =
run with a larger window size, but it will actually make things go =
slower.

It was naively increasing the maximum window size to 255 that caused the =
huge performance problems in the 1.5.x series that Andrei highlighted at =
the 2010 European AFS workshop.

S.