Re: [RESEND RFC PATCH V3] sched: Improve scalability of select_idle_sibling using SMT balance

Peter Zijlstra
2018-02-05T17:04:16Z

On Mon, Feb 05, 2018 at 01:48:54PM +0100, Peter Zijlstra wrote:
> So while I see the point of tracking these numbers (for SMT>2), I don't
> think its worth doing outside of the core, and then we still need some
> powerpc (or any other architecture with abysmal atomics) tested.

FWIW Power has another 'fun' feature, their cores have asymmetric SMT.

Their cores have a static power level, based on _which_ SMT sibling is
running, not how many. A single SMT2 runs (much) slower than a single
SMT0.

So that random selection stuff really doesn't work well for them. Now
'sadly' x86 can also have ASYM_PACKING set on its SMT domain, so I'm
going to have to figure out what to do about all that.