prof question

[gwyn%brl-vld at sri-unix.UUCP]

From:      Doug Gwyn (VLD/VMB) <gwyn at brl-vld>

Profiling samples one's process every so often (clock tick typically)
and records where the PC (program counter) is each sample.  This data
is stored as a histogram with "bin width" usually equal to several
bytes.  The "quantization errors" can take three forms:
	- All PC locations within a bin are counted together;
	- Since the sampling is periodic it may not be representative
	  of the real PC distribution due to beating with code
	  periodicities (especially if code and sampling are driven by
	  the same clock);
	- Because the code is sampled rather than exhaustively traced,
	  some sections can be missed, and in general Poisson sampling
	  statistics apply (i.e. sampling error for a bin is roughly
	  the square root of the bin count).

Each subroutine on "prof" output summary includes only the time spent
in its PC range, so a call to another routine will result in time
spent in the called routine being tallied under its name rather than
under the caller's name.