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

[Nicholas Piggin]

On Wed, 05 Apr 2017 07:01:57 -0700 (PDT)
David Miller <davem at davemloft.net> wrote:

> 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.
> 

Thanks for taking a look. The default spin primitives should just
continue to do the right thing for you in that case.

Arm has a yield instruction, ia64 has a pause... No unusual
requirements that I can see.

If there are no objections, I'll send the arch-independent part of
this through the powerpc tree (the last one I sent, which follows
Linus' preferred pattern).

Thanks,
Nick