[ofa-general] How many processes on a node can open IB device ?

[Roland Dreier]

 > I have simple IBV code, which only open the device and create PD.
 > (attached below), then the code sleep there.
 >
 >  When I start as many processes as I could, it fails at 895 copies, it fails with error:

That sounds right for mlx4 with default firmware on a 4KB page size (ie
x86) system.  There are 1024 pages of user access registers available,
but 128 + 1 = 129 are reserved for internal driver use.  So that would
leave 895 available for userspace use, exactly as you found.

You should be able to build firmware that supports more processes, but
I believe there may be some performance/stability tradeoffs related to
that -- Mellanox could tell you more.

 - R.