On Sat, Jun 25, 2022 at 08:57:35AM +0900, Akira Yokosawa wrote: > On Fri, 24 Jun 2022 16:33:16 -0700, Paul E. McKenney wrote: > > On Sat, Jun 25, 2022 at 08:12:09AM +0900, Akira Yokosawa wrote: > >> Hi Paul, > >> > >> I find the analogy of Figure 7.11 hard to grasp. > >> > >> Whether a lock is global or per-instance, the cost of locking > >> (saw kerf) is observed only when a CPU/thread does the locking > >> operation. > >> > >> In this figure, does each board represent data elements, not a > >> CPU/thread? If this is the case, what does the waste of "saw kerf" > >> mean? > >> > >> What am I missing? > >> > >> (I hope I am clear enough on what I don't get...) > > > > It might well be that I am getting too excited about this one. ;-) > > > > Maybe I need to drop it. At the very least, I need to much more clearly > > explain it. > > > > But... > > > > Each board represents one lock. The "saw kerf" is the time lost when > > releasing that lock and someone else immediately acquiring it. > > > > Does that help? > > Well then, why does the left side figure have ten boards? Ten locks. For example, the single board might correspond to a hash table guarded by a single global lock. The ten boards might correspond to a hash table with ten buckets, with per-bucket locking. But it is sounding like this analogy might be more confusing than enlightening. Thanx, Paul
