> Hmmm, nowhere in the patch is the actual reason this is
> needed explained.  Could you have some of that?

Good idea, Pedro. How's the attached?

+  /* Try using the frame stash first.  Finding it there removes the need
+     to perform the search by looping over all frames, which can be very
+     CPU-intensive if the number of frames is very high (the loop is O(n)
+     and get_prev_frame performs a series of checks that are relatively
+     expensive).  This optimization is particularly useful when this function
+     is called from another function which already loops over all frames,
+     making the overall behavior O(n^2).  */

-- 
Joel