[openib-general] [PATCH] use mmiowb after doorbell ring

[Roland Dreier]

 > Well, at startup we can read /proc/cpuinfo and look for sse2 in the flags: line.
 > Seems simple enough.

Detecting SSE2 is easy -- we could just do the cpuid ourselves if we
wanted to.  The problem is what do you do when you see that the CPU
does or doesn't have the instruction?  The runtime patching that the
kernel does is way too complicated, and if you're going to move mb()
out of line then just doing a regular serializing instruction is
probably just as good.

 > I hope we can do something without compile flags - most people
 > don't know enough to turn them on, and distros commonly
 > compile for least common denominator.

And rightfully so -- the default compile of libibverbs/libmthca should
run on a least common denominator CPU.

 - R.