Re: wire rate vs UDP throughput
Marc:
how do you figure/calculate the number 22 Mbps from
what I am sending ??
12/54 ?? this is the efficiency of USER-DATA v/s DATA-ON-WIRE
I think that would mean 22Mbps at the UDP level, but If I use
Iperf with -b 100m (UDP level desired byte rate),
then Iperf is not obeying me ?? ;)
I use: iperf -c IP_PC2 -u -w 200k -l 12 -n 1785708 -b 100m
(which would lead to 148809 frames/s at 100mbps)
are some of these options mutually excluyent ??
thanks for your input...
Marc Herbert wrote:
> On Fri, 30 Jul 2004, Marcelo Maraboli wrote:
>
>
>>>Headers in this case are 42 bytes long (just tested on loopback). So
>>>with -l 12, packets are 54 bytes long, so you can get at most...
>>>22Mb/s. Quite different from 100M (or event 90M) indeed.
>>
>
> You are probably right; I just made a quick test on the loopback
> interface to get an idea.
> The argument still is: with small payloads, the proportion of headers
> is huge, and the throughput at the UDP level is very far from the wire
> rate.
>
>
>
> The iperf interface allows you to specify the throughput at the
> UDP level, not the throughput on the wire. You have to compute the
> former from the latter (just like we did above). I think some guy
> asked for this feature some months ago (check the archive). This is
> just "too hard" to implement since iperf has no knowledge about lower
> layers. A common case (IP, Ethernet) could be implemented, but this
> would be quite dirty IMHO.
>
> On the other hand, if you just want "full wire speed", you just have
> to configure your sending system to avoid drops on the sender (on
> linux, you just have to check that -w SND_BUF << ifconfig txqueuelen),
> and then you just ask "full speed" to iperf, that is: iperf -b 2G.
>
> Also try to keep queues small to avoid jitter. For instance set both
> SND_BUF and txqueuelen at relatively small values on linux.
>
> Cheers,
>
> Marc.
>
>
--
Marcelo Maraboli Rosselott
Jefe Area de Redes (Network & UNIX Systems Administrator)
Ingeniero Civil Electronico (Electronic Engineer)
Direccion Central de Servicios Computacionales (DCSC)
Universidad Tecnica Federico Santa Maria, Chile.
phone: +56 32 654237
mailto:marcelo.maraboli --at-- dcsc.utfsm.cl http://elqui.dcsc.utfsm.cl/