[lwip-users] [lwip] Re: [lwip-members] Suggestion: define TMR constants in lwipopts.h instead of tcp.h

[Kieran Mansley]

On Thu, 24 Oct 2002, Chris Borrelli wrote:

>
> Suggestion: It would be nice if TCP_TMR_INTERVAL, TCP_FAST_INTERVAL, and
> TCP_SLOW_INTERVAL were defined in the lwipopts.h instead of (or as well
> as) tcp.h
>
> Decreasing these values really seems to increase the performance of the
> stack at 100Mbps.  I have these values set to 1, 2, and 5 respectively
> in my v2pro port and it dramatically increased transmit throughput.

Interesting.  It seems as though there is some problem with ACKs not being
sent if you really see such a large increase in performance.  It sounds as
if ACKs are being delayed waiting for data to piggyback on, none is
arriving, and so it waits for a fast timer timeout before sending it
anyway.  Is your application largely uni-directional traffic?

The values you have put are very small, and it should be possible to
achieve 100Mbps rates without having the large overhead of timers every
millisecond.  The values are meant to be a trade off between latency,
bandwidth, and CPU.  Setting them to very small values gives good latency,
which increases the bandwidth by preventing the window closing, but at the
cost of increased CPU usage.

> Putting these into the lwipopts.h allows different arch ports to set
> these values without changes to the core files.

Seems like a reasonable suggestion, certainly to allow people to
experiment.  The default values shouldn't change though.

Kieran

[This message was sent through the lwip discussion list.]