On Tue, Apr 21, 2009 at 08:41:36AM +1000, Paul Mackerras wrote: > Paul E. McKenney writes: > > > But a single CPU is acquiring one lock per CPU, so all the increments > > are to one CPU's preempt_count. :-( > > OK, I see, so a task can't take more than 255 spinlocks without > overflowing the preempt count, which seems a bit limiting. > > There are 6 free bits in the preempt_count currently, so the preempt > count could be expanded to 14 bits, which would be enough for all > current systems. Beyond that I guess we could make preempt_count be a > long and allow bigger counts on 64-bit architectures. Or we use the trick Eric suggested and Steve employed in the most recent patch. ;-) An alternative would be for the update code to acquire but one lock at a time, but this would likely require another lock to exclude other updaters and I believe would also require restructuring the count accumulation. So Steve's current patch seems a bit less intrusive, overall. Thanx, Paul -- To unsubscribe from this list: send the line "unsubscribe netfilter-devel" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
