> Well, there are some time-tick events. E.g. Intel Core 2 has the
> CPU_CLK_UNHLATED:REF event, that is described by Intel in the following
> way:
>
> But when I try to use interval sampling in pfmon, with sample period set to
> 100 ms,
> the counts of this event oscillate, sometimes with differences even 100x -
> 1000x.

I'm not sure if it's causing this particular problem for you, but check
the intel errata.  There's one for this perf counter that makes the count
vary with system frequency on some machines.  A core2 machine we have
exhibits this erratum.

I don't think that would cause a 100x difference though.

See the document here:
  http://www.intel.com/design/mobile/specupdt/314079.htm
especially #ah99 though there are many other perf counter issues in that
document.

Vince



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