Re: [PerfSuite-users] monitoring the same process

[Rick K. <rk...@nc...>]

On Tue, 10 Jan 2006, Giuseppe Grieco wrote:

> I would like to know why it happens that monitoring the same process, 
> the number of total floating point operations changes.
> I guess it should remain the same. Is it?
> Thanks, Giuseppe

Giuseppe,

I think it depends on a number of factors.  If you are using default 
configuration files for PerfSuite, remember that multiplexing (timesharing
of the available performance counter registers) will be occurring.  By
nature this results in estimates of the true number of event occurrences
and will be inexact, so the counts can be expected to vary from run to 
run.

Also, depending on the CPU type and the underlying access method (Perfmon
or PAPI), the "floating point operation" count may also include vector
operations (e.g. x86 SSE), which are not all strictly floating point
operations.  Some things are compiler-dependent.

Finally, things can vary to some extent just to different runtime 
conditions although it's hard to say since you don't indicate to what 
degree you are seeing variation.

Rick