MFC r266171, r266174 by gnn:

  Update the amount of data we can collect for hwpmc(4) by default
  to work with modern processors and available memory.

  Upgrade the default callchain depth

Approved by:	re
MFC r267090:

Correct the document date for last change.

Approved by:	re (gjb)
MFC r266166 by gnn:

  Extend the size of the function or symbol that can be annotated.

Approved by:	re
MFC r266903:

  Update default callchain depth to 16 to match kernel

Approved by:	re