On Thu, Dec 22, 2011 at 09:17:57AM +0100, Andi Kleen wrote: > The costly operations here are the atomics and nothing really changes > for them. So I don't expect any measurable difference. > > I actually have an idea to remove them for the common case, but not in > that patchkit or cycle :) > > I can run a ftrace if you want, but I expect any difference to be below > the measurement inaccuracy. What I'm concerned with is not the cost of extra dereference per se; it's more about cacheline bouncing - note that with this fix in place you'll end up with spinlock in the same cacheline as the pointer to per-cpu stuff. Hell knows; it might not matter at all, since we take it only for br_write_lock() (and definitely rare CPU up/down), but still, I'd like to see the data. In any case, that's not -stable material. The race fix, OTOH, is... -- To unsubscribe from this list: send the line "unsubscribe linux-fsdevel" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
