Schedule granularity

[Brecht Vermeulen]

Benjie,

yes, that's a nice one !

Just what we needed, but what time resolution could be possible ?

So, the DelayShaper is put between a queue and a ToDevice I believe as a
pull element and it only returns a packet if one is ready. Do you have
an idea how many times this element would be called in a normal
configuration and how small the interval can be, is e.g. somehting in
the order of 50us possible ?
(have you benchmarks on this ?)

regards,
Brecht

PS. GUI is coming up soon :-)

Benjie Chen wrote:
> 
> in the latest click release there are two elements that could be
> useful for you. they are DelayShaper and DelayUnqueue.
> 
> both elements can be used to simulate latency across a wire.
> they emit a packet only if the packet has been delayed for a
> specified amount of time. right now they both take ms arguments,
> but you should be able to change them to be us arguments easily.
> 
> you must use them with the SetTimestamp element, which sets the
> timestamp annotation of the packet. you should set the timestamp
> when the packet comes into the configuration. SetTimestamp uses
> gettimeofday for timestamp. gettimeofday uses the timestamp/cycle
> counter on the chip to get the time, so i believe everytime you
> call it you will get a different value. check arch/i386/kernel/time.c
> for detail...
> 
> hope this is what you needed...
> 
> On Tue, Jul 03, 2001 at 05:15:52PM +0200, Brecht Vermeulen wrote:
> >
> > Dear Click'ers,
> >
> > Has anyone a fine idea about the time granularity which can be used in a
> > Click element ?
> >
> > The issue is that other people in the project ask to simulate a network
> > between 2 routers (which will be click routers) with a.o. delay.
> >
> > So, it is possible to develop a delay Click element, but what timing
> > resolution can be used, or how can we e.g. make the packet delay a
> > certain time (I don't know very much about the Linux kernel) ?
> >
> > I know normally the kernel has a scheduling granularity of 10 ms (100
> > Hz). Is click also dependent of this or how do you schedule the
> > different elements ?
> >
> > thanks for any help,
> > Brecht
> 
> --
> benjie chen
> benjie at lcs.mit.edu