Hello,
some new observations to my previous message:
> * Do you think method b) can be better than a) in some
> circumstances? I haven't found a "timer tick" event in pfmon, so I
> would use the count of instructions. It is then clear that different
> cores will process different amount of instructions per-second, so I
> loose the time semantics, however I should still have relative
> timing to the one core.
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:
This event is not affected by core
frequency changes (e.g., P states, TM2
transitions) but counts at the same
frequency as the time stamp counter. This
event can approximate elapsed time while
the core was not in halt state.
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.
How can this be explained?
Thank you very much!
Tom
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