On Tue, Mar 09, 2021 at 07:46:11AM -0800, Davidlohr Bueso wrote: > On Tue, 09 Mar 2021, Michal Such�nek wrote: > > > On Mon, Mar 08, 2021 at 05:59:50PM -0800, Davidlohr Bueso wrote: > > > 49a7d46a06c3 (powerpc: Implement smp_cond_load_relaxed()) added > > > busy-waiting pausing with a preferred SMT priority pattern, lowering > > > the priority (reducing decode cycles) during the whole loop slowpath. > > > > > > However, data shows that while this pattern works well with simple > > ^^^^^^^^^^^^^^^^^^^^^^ > > > spinlocks, queued spinlocks benefit more being kept in medium priority, > > > with a cpu_relax() instead, being a low+medium combo on powerpc. > > ... > > > > > > diff --git a/arch/powerpc/include/asm/barrier.h > > > b/arch/powerpc/include/asm/barrier.h > > > index aecfde829d5d..7ae29cfb06c0 100644 > > > --- a/arch/powerpc/include/asm/barrier.h > > > +++ b/arch/powerpc/include/asm/barrier.h > > > @@ -80,22 +80,6 @@ do { > > > \ > > > ___p1; \ > > > }) > > > > > > -#ifdef CONFIG_PPC64 > > Maybe it should be kept for the simple spinlock case then? > > It is kept, note that simple spinlocks don't use smp_cond_load_relaxed, > but instead deal with the priorities in arch_spin_lock(), so it will > spin in low priority until it sees a chance to take the lock, where > it switches back to medium.
Indeed, thanks for the clarification. Michal