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Re: TC calling sequence timing

Let me give you the script that generates this results, even if I believe this
behaviour is not depended at
the tbf parametrs but really at the scheduling and interupt mechanics of
linux. I also must point out that this behaviour is not really a problem,
because if other streams exist, as in a router, since packets from other
streams enqueued will trigger the dequeue function of the device. But anyway
is not the anticipated behaviour from what I have understand about kernel and
tc so any conversation on it will clarify the kernel operation.

tc qdisc add dev $DEV handle 1:0 root tbf rate 80Kbps buffer 3Kb limit 40Kb
DEV=atm0 or eth0 (it has been tested with both)

the tg script that generates traffic is
on 0:4
at 12 setup
at 13 arrival constant 0.05 length constant 800
packet 200

jamal wrote:

> Panagiotis,
> On Mon, 3 Apr 2000, Panagiotis Stathopoulos wrote:
> > Hello all,
> > I would write about a bug or let's say a special behavior that exists in
> > the call sequence of the tbf qdisc and I imagine in general in the
> > kernel traffic control call sequence.
> > (Configuration: kernel 2.2.13, iproute 990630, ds 6, atm0.59)
> > I am working on a modified version of tbf and i have noticed the
> > following behavior:
> > If the incoming to the tbf shaper rate exceeds the tbf rate, more
> > packets come in from the ones tbf can transmit, the call of the enqueue
> > function triggers correctly the dequeue fuction, that is; dequeuing of
> > packets occurs at the time stamps that should. (lets say for a 1024
> > timer, packet size 800, tbf rate = 80kbps, incoming packet rate 160kpbs
> > we have a packet transition at a period of 10ms). (tg was used as a
> > traffic measurement & genetation tool)
> TBF is influenced by quiet a few parameters; peakrate, rate, MTU, burst
> size etc. It will do what you ask it to ;-> And at times it will let
> bursts flood the gate i.e you might end up sending at wire speed.
> What are your parameters like?
> cheers,
> jamal

Panagiotis G.Stathopoulos
National Technical University of Athens
Telecommunications Laboratory
E-mail: pstath@telecom.ntua.gr
Tel: +30 1 772 1479     Fax: +30 1 772 2534