Re: [RFC] setting up throughput threshold indications to userspace

[Luciano Coelho <luciano.coelho@nokia.com>]

On Mon, 2010-08-16 at 17:19 +0200, ext Jan Engelhardt wrote:
> On Monday 2010-08-16 16:01, Luciano Coelho wrote:
> >> You can implement a daemon: which samples the statistics data of NIC
> >> periodically, calculates the average bandwidth in a period, and change
> >> the condition variables accordingly.
> >
> >We don't want to use polling from userspace.  That's the reason why we
> >decided to use iptables instead.  The idea is that we will only notify
> >the userspace when the throughput crosses the threshold line.  And the
> >rules I defined above are working rather well, except for this "detail"
> >that the BELOW signal is not sent when there's no data flowing.
> 
> Without data, the turing machine won't finish, so you can't say for
> sure that you reached below. That is sort of a halting problem, which
> is known to be unsolvable.

Yes, that's the theoretical way to put it.  :) In practice I see that
without data the rules won't be traversed and therefore we can't make
any rate calculations.

But if I add an idletimer (which uses a timer to trigger execution,
regardless of the availability of packets to process) with a timeout
equal to the estimator's measurement averaging interval (ewmalog), I can
be sure that the rate went to 0 bps if the timer expires.  Ie. no
packets at all during the measurement interval means 0 bps, right?

-- 
Cheers,
Luca.