[openib-general] Fw: openib-general Digest, Vol 30, Issue 135

[Michael S. Tsirkin]

First, please avoid answering the digest. This breaks threading in most mailers.

> > > >
> > > > Tried this patch, it didn't work on ehca. I couldn't change the mode from
> > > > datagram to connected from /sys/class.
> > >
> > > It's wroking as designed in that respect.  ehca does not implement
> > > srq - without
> > > srq, there is no way to prepost receive buffers for a resonable number of
> > > connections without running out of memory.
> > >
> > > So it is falling back on datagram mode.
> > > Talk to ehca guys to implement srq and connected mode will be enabled.
> > Don't remember SRQ is a MUST for UC mode. Does this patch support
> > devices with SRQ in RC mode?
> 
> I don't think the IB HCA Spec requires SRQ support for RC but is an optional
> feature. There are two adapters right now that don't support SRQ which means to
> use IPoIB-CM on them you should make the use of SRQ an option setting.

No, adding such "drink up all memory on real clusters but run well on a back to back
benchmark platform" option does not seem like a good idea to me.
Rather, we should use UD mode to keep IPoIB scalable on all hardware.

> I agree
> that if it is available it should be used for scaling issues probably if
> available automatically set. But I would like to see us at least support the
> current hardware that meets the current SPEC.

SRQ support is clearly optional. But neither is IPoIB CM support a required
feature. Current code will fall back to datagram mode when SRQ is not
supported, and since UD support in not optional, all current hardware is still
supported with IPoIB - this patch does not break this.

-- 
MST