[Info-vax] How to obtain percentage of a given CPU consumed by a process

[johnwallace4 at yahoo.co.uk]

On Saturday, 4 June 2016 20:17:52 UTC+1, Hans Vlems  wrote:
> I'll bite: how?

There may be a strong hint in the wording: "whilst *recording* minimal
CPU time".

Is *recording* CPU time in the usual OS-provided way guaranteed to
produce a result which will be the same time (give or take a little
bit) as the actual *used* CPU time?

Generally not, on VMS or elsewhere, on VAX or elsewhere, though
on Alpha the RPCC instruction provided an interesting approach to
accurately seeing how much processor time a process has really
used. Maybe x86-64 has something similar by now, maybe ARM also.


I can't remember whether the approach I'd use can be done just with
non-priv code, but I'm pretty sure I have done it, as an exercise in
demonstrating that trusting the usual tools is a good start, but not
always reliable.

Let's see what people come up with. Have a lot of fun. Back in a 
while...