[openib-general] mwrite64 - need for uar object in access layer

[Roland Dreier]

    Troy> How does just using the floating point unit compare the the
    Troy> SSE codepath? In a past life I had to get a flash driver for
    Troy> a 32 bit PPC board working that *had* to have 64 bit access
    Troy> to flash.

It's a pretty huge loss, because saving/restoring the FPU state
requires writing/reading something like 170 bytes.  With SSE we can
just save the 8 bytes of XMM register that we actually use.  Even so
I'm not convinced SSE is a win over just using a lock because saving
CR0 is so expensive.

As I said, I'd be curious to see benchmarks of other approaches.  I
think there's definitely room for improvement if someone is interested
in working on this.

 - R.