Re: [RFC PATCH 0/7] Share events between metrics

On Thu, May 07, 2020 at 10:43:43PM -0700, Ian Rogers wrote:

On Thu, May 7, 2020 at 2:47 PM Andi Kleen [off-list ref] wrote:

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- without this change events within a metric may get scheduled
  together, after they may appear as part of a larger group and be
  multiplexed at different times, lowering accuracy - however, less
  multiplexing may compensate for this.

Does mutiplexing somewhat related events at different times actually reduce
accuracy, or is it just more likely to give that appearance?

It seems that perf measurements are only useful if the workload is in a
fairly steady state.  If there is some wobbling, then measuring at the
same time is more accurate for the periods where the events are being
measured simultaneously, but may be far off for when they are not being
measured at all.  Spreading them out over a longer duration may actually
increase accuracy by sampling over more varied intervals.

Or, is the concern more about trying to time-slice the results in a 
fairly granular way and expecting accurate results then?

(Or, maybe my ignorance is showing again.  :-)

PC