[openib-general] [RFC/BUG] libibverbs: DMA vs. CQ race

[Roland Dreier]

 > Can we get back to this problem? I understand that the way ehca does
 > things is not acceptable, so is seems that ehca people will also have
 > to rethink how CQ/QP memory is allocated. It would be a good idea to
 > consolidate solution for mthca and ehca. mmap() special allocator can be 
 > added to fd libibverbs uses for communication with the kernel and it can
 > be used by all low level drivers (I don't know if such a way is
 > acceptable for echa). The question is if this is a good idea to add
 > something as general as coherent memory allocation for userspace (which
 > is needed by other userspace drivers) to infiniband subsystem.
 > 
 > What do you think?

I think that's kind of overengineering things.  Allocating and mapping
memory in an mmap method is just a few lines of code so we might as
well let drivers do exactly what they want.

I think the bigger problem is fixing the kernel so it's easier for
drivers to specify the page attributes they want for memory mapped to
userspace (eg uncached, magic altix "OK for DMA", write combining, etc)

 - R.