[perfbook] Analogy of Figure 7.11 Locking “Saw Kerf”

[Akira Yokosawa <akiyks@xxxxxxxxx>]

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...)

        Thanks, Akira