[Tech] LIFO simulations

[Matthew Toseland]

On Thu, Dec 14, 2006 at 06:35:32PM +0000, Michael Rogers wrote:
> toad wrote:
> >>> Are you allowing *ALL* requests
> >>> to complete before reporting the result?
> >> No, I'm taking a slice of the simulation in its steady state and 
> >> counting the number of messages sent and received in that slice.
> > 
> > If it is actually a steady state - is it?
> 
> It's hard to be sure. FIFO seems likely to reach a steady state quite 
> quickly because nothing stays in the network for very long, especially 
> with short queues. But with LIFO I'd imagine it's possible for packets 
> to sit at the bottom of the queue for a very long time. 

Which is precisely why LIFO sucks... FIFO has a more or less fixed
latency for a given load, it forces requests to wait in line. Whereas
LIFO encourages anti-social behaviour such as cancelling and trying
again every 10 seconds. So it's not practical - but I'm very surprised
that we are getting apparently good results for it.

> I'd have to run 
> a lot of repetitions and check that the first half of the slice wasn't 
> distinguishable from the second half.
> 
> Cheers,
> Michael
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