On Thursday 16 August 2012, Will Deacon wrote: > > > + > > > +#include <linux/kernel.h> > > > +#include <linux/spinlock.h> > > > +#include <linux/atomic.h> > > > + > > > +#ifdef CONFIG_SMP > > > +arch_spinlock_t __atomic_hash[ATOMIC_HASH_SIZE] __lock_aligned = { > > > + [0 ... (ATOMIC_HASH_SIZE-1)] = __ARCH_SPIN_LOCK_UNLOCKED > > > +}; > > > +#endif > > > > What? > > > > I suppose this is a leftover from an earlier version using the > > generic bitops, right? > > We currently use the generic atomic bitops (asm-generic/bitops/atomic.h) > which contains: > > # define ATOMIC_HASH(a) (&(__atomic_hash[ (((unsigned long) > a)/L1_CACHE_BYTES) & (ATOMIC_HASH_SIZE-1) ])) > > so we have to provide a definition for the array. We have additional patches > containing optimised assembly implementations of the atomic bitops which we > will push later, once we've got some hardware to benchmark with. >
Ah, I was confusing this with the asm/atomic.h stuff, for which you already provide an optimized version. The generic atomic bitops are really horrible in performance and I would expect that there is just one obvious way to implement bitops using ldaxr/stlxr, so I recommend just doing that even if you have no hardware for benchmarking. The s390 version should be fairly easy to adapt. Arnd -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/