Re: infiniband limit of 32 cards per system?

Alex Chiang
2010-01-26T03:59:06Z

* Roland Dreier <rdreier@cisco.com>:
>
> > My colleague points out the following enum in uverbs_main.c:
> >
> > enum {
> > IB_UVERBS_MAJOR = 231,
> > IB_UVERBS_BASE_MINOR = 192,
> > IB_UVERBS_MAX_DEVICES = 32
> > };
> >
> > Experimentally, we've determined that on a system where we
> > plugged in 40 IB cards, OFED only reports 32 cards are present.
>
> wow, 40 HCAs in one system !

HP sell some pretty big systems. :)

> > If that enum is indeed the limiting factor, would someone mind
> > explaining (or pointing me at TFM ;) why it's limited to 32
> > devices?
>
> That dates back to when device #s had 8 bits for major and 8 bits for
> minor. We got one major assigned for IB, and had to split up the 256
> minors that gave us among userspace verbs, management access, etc. And
> 32 seemed like a pretty reasonable limit for most uses.

Thanks for the explanation.

> Nowadays I guess we should look into expanding that to dynamic device
> numbers on overflow, assuming you do have a realistic situation where
> someone would want to use that many adapters per system.

Think of a large scale-up ia64 box, possibly running some
virtualization stack.

I'm guessing that it's not just a simple kernel fix though since
OFED has to change too, right?

/ac