[e2e] Packet transmission timer

[Luigi Rizzo]

> > In a rate based transport scheme, the inter packet gap is fixed
> according to the rate at which we want to deliver the packets. I
> do realise that for, say, MBits/s transmission of 1000 bytes packet
> size, this inter packet gap will be somewhere around milliseconds
> or less. But most OSs are not able to provide that of a high timer
> resolution. I am only able to obtain at most a 10ms granularity.
> This is certainly insufficient but I am sure people have worked
> around this constraint. I was just wondering if there is anyone on
> the list who could advise me on this. What is the most common
> implementation technique of the timer for these rate control method?
> How do I achieve MBits/s delivery rate on a Windows platform or a
> Linux platform? I thank you in advance.

as long as you make sure not to accumulate the scheduling errors,
(basically, read the clock after sleeping and see how much you
should really send), you will have some burstiness in the
output.

This is the best you can do given the timer limitations and unless
you want to do busy waiting (or you can do something useful betwen
the transmission of subsequent packets, which can be a meaningful
options if e.g. you have also to encode the content you are going
to transmit).

I guess on most unixes you can tweak the timer granularity by
recompiling a kernel with a different value for the HZ variable.

	cheers
	luigi