On Fri, 2013-02-22 at 15:16 +0100, Ingo Molnar wrote: > > I checked arch/x86/include/asm/atomic64_32.h and we use > > cmpxchg8b for everything from _set() to _read(), which > > translates into 'horridly stupendifyingly slow' for a number > > of machines, but coherent. > > That's a valid concern - and cmpxchg8b is the only 64-bit op > available on most 32-bit x86 CPUs which does not involve the > FPU. > > Wondering how significant this range of x86 problem boxes will > be by the time any of these changes reaches upstream and distros > - and how much 'horridly stupendifyingly slow' is in terms of > cycles expended.
On the !x86 side of things we're implementing (generic) atomic64 using hashed spinlocks, so there too using a single spinlock around the entire data structure is a complete win. -- 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/
