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

[Roland Dreier]

 > > Another confusing thing is that asm-i386 defines mb() and rmb() just
 > > to be compiler barriers,
 > 
 > I see:
 > #define rmb() alternative("lock; addl $0,0(%%esp)", "lfence", X86_FEATURE_XMM2)

Oops, you're right.  I misread that file.

OK, we probably want mb() to be more than a compiler barrier on i386
and x86-64.  I'll fix up the libibverbs code.

 > as for mb() - I don't thnk our kernel code uses that so I think userspace
 > should switch to wmb as well. wmb isjust a compiler barrier on most
 > arhitectures.

I'm not sure it's worth the trouble to split up the two cases at this
point.  Does it make a bit performance difference?

 - R.