[RFC][PATCH] spin loop arch primitives for busy waiting

[David Miller]

From: Nicholas Piggin <npiggin at gmail.com>
Date: Tue, 4 Apr 2017 13:02:33 +1000

> On Mon, 3 Apr 2017 17:43:05 -0700
> Linus Torvalds <torvalds at linux-foundation.org> wrote:
> 
>> But that depends on architectures having some pattern that we *can*
>> abstract. Would some "begin/in-loop/end" pattern like the above be
>> sufficient?
> 
> Yes. begin/in/end would be sufficient for powerpc SMT priority, and
> for x86, and it looks like sparc64 too. So we could do that if you
> prefer.

Sparc64 has two cases, on older chips we can induce a cpu thread yield
with a special sequence of instructions, and on newer chips we have
a bonafide pause instruction.

So cpu_relax() all by itself pretty much works for us.