[openib-general] question on QoS support

[Feiyi Wang]

In our test at the ORNL - it appears you can "turn off" the traffic by
giving every VL weight 0. As soon as you assign non-zero VL weight,
the traffic starts to flow, however, VL with more weight doesn't have
expected preference treatment. In other words, traffic shaping didn't
take place. smpquery vlarb verified the mapping table was there.

I believe the scenario described below 'should' be able to generate
congestion point ... but it would be helpful if someone can elaborate
a way to "look into" how/if scheduling/arbitration take place.

Best,

Feiyi


On 02 Nov 2006 10:49:04 -0500, Hal Rosenstock <halr at voltaire.com> wrote:
> Hi Oliver,
>
> On Thu, 2006-11-02 at 10:20, Oliver wrote:
> > Hi, Hal -
> >
> > > How is this being observed/measured ?
> >
> > Host A, B, with 4x DDR both connected to Flextronic switch.
> > A single process of ibv_read_bw gives about 1415MB /s average
> > bandwidth. Two concurrent process report 714.45 MB/s each, dead even.
> > Now if I bump up one process with a different SL, then I expect to see
> > shaping to take place. Please let me if the scenario makes sense.
>
> It makes sense. However, if the higher priority traffic does not fill
> the scheduling, the low priority can take up the slack so I'm not sure
> if this is what you are seeing or something else.
>
> It might be interesting to try the same thing at SDR speeds.
>
> -- Hal
>
> > > Yes, 8 VLs should be supported in your subnet. You can verify this with
> > > smpquery portinfo on the HCA port and examine OperVLs assuming the port
> > > is ACTIVE.
> >
> > yes, I verified the data VL support, it is 8. I will poke for more
> > info with suggested commands by Sasha.
> >
> > > > A related question is, if I modify qos setting in SM, do I need to
> > > > restart SA on each hosts for it to see the changes? (I am hoping not,
> > > > as I tried in the test, it doesn't seem to make a difference)
> > >
> > > Not sure what you mean. SA is tightly coupled with the OpenSM. Do you
> > > mean SA client ? The client hosts don't need restarting but did you
> > > restart OpenSM with your QoS configuration ?
> >
> > I mean client SA. yes, I understand OpenSM needs to be restarted.
> >
> > > BTW, which OpenSM are you running ?
> >
> > OFED 1.1 based.
> >
> > thanks
> >
> > - Oliver
>
>