Re: [PATCH v2 1/3] sched: Stop nohz stats when decayed

[Peter Zijlstra]

On Thu, Feb 08, 2018 at 03:30:31PM +0000, Will Deacon wrote:
> On Thu, Feb 08, 2018 at 03:00:05PM +0100, Peter Zijlstra wrote:

> > Without this ordering I think it would be possible to loose has_blocked
> > and not observe the CPU either.
> 
> I had a quick look at this, and I think you're right. This looks very much
> like an 'R'-shaped test, which means it's smp_mb() all round otherwise Power
> will go wrong. That also means the smp_mb__after_atomic() in
> nohz_balance_enter_idle *cannot* be an smp_wmb(), so you might want a
> comment stating that explicitly.

Thanks Will. BTW, where does that 'R' shape nomenclature come from?
This is the first I've heard of it.