On Thu, Jun 21, 2012 at 08:35:48AM +1000, Dave Chinner wrote: > writes are single instructions on 64 bit systems. The lock is > required for 32 bit systems because the write requires separate 32 > bit writes to the LSN which can result in unlocked accesses seeing > partially updated (and hence incorrect) LSN values. > > So the memory barriers are definitely needed for 64 bit machines > because there is no locking on the update and spinlocks only provide > memory barriers via unlock->lock transitions, not via a single > spin_lock() call. Indeed. So we'll either need the barriers, or just always take xa_lock in xfs_ail_push. Given that xa_lock and xa_target appear in the same cache line it probably wouldn't even make much of a difference. _______________________________________________ xfs mailing list xfs@xxxxxxxxxxx http://oss.sgi.com/mailman/listinfo/xfs
