From: Peter Zijlstra <pet...@infradead.org> Date: Fri, 19 May 2017 11:03:02 +0200
> On Thu, May 18, 2017 at 10:31:13PM -0400, David Miller wrote: >> From: Babu Moger <babu.mo...@oracle.com> >> Date: Thu, 18 May 2017 18:36:08 -0600 >> >> > @@ -82,6 +82,7 @@ config SPARC64 >> > select HAVE_ARCH_AUDITSYSCALL >> > select ARCH_SUPPORTS_ATOMIC_RMW >> > select HAVE_NMI >> > + select ARCH_USE_QUEUED_RWLOCKS >> > >> >> If you are selecting this on SPARC64 all the time, then: >> >> > @@ -94,6 +94,7 @@ static inline void arch_spin_lock_flags(arch_spinlock_t >> > *lock, unsigned long fla >> > : "memory"); >> > } >> > >> > +#ifndef CONFIG_QUEUED_RWLOCKS >> > /* Multi-reader locks, these are much saner than the 32-bit Sparc ones... >> > */ >> >> You can remove this segment of ifdef'd code altogether since it is in >> a sparc64 specific header file. > > > So IIRC Sparc v8 only has that single byte load-and-set (or swap) > instruction, right? That means you can only make test-and-set spinlocks > and then have to build the world on top of that. > > I don't see qrwlock -- which assumes the spinlock implementation is fair > -- making much sense for that. > > Also, IIRC Sparc-v8 didn't really have very big SMP systems, those came > with v9. And qspinlock only really makes sense on the bigger systems > (not to mention that building the qspinlock on top of atomic operations > build on test-and-set spinlocks just seems extremely dysfunctional). > > > In any case, I think what I'm saying is that it makes sense to make this > a Sparcv9 only feature. I agree with you, there is no reason to try and support queued locks on 32-bit sparc. However, I don't see what any of this has to do with the feedback I was giving the patch author :-)
