Dueling performance monitors
Dueling performance monitors
Posted Dec 10, 2008 15:59 UTC (Wed) by deater (subscriber, #11746)In reply to: Dueling performance monitors by jreiser
Parent article: Dueling performance monitors
How fine-grained are you looking? If you are getting so fine-grained that an extra syscall makes a difference, then you are probably starting to run into issues with skid. Not to mention if you are trying to read multiple counters at the exact same time.
Posted Dec 10, 2008 21:02 UTC (Wed)
by jreiser (subscriber, #11027)
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Dueling performance monitors
As fine grain as every subroutine call and return. Some routines do encounter issues with variance due to in-flight instructions and overhead due to shortness. Usually the issues are visible and specific, and can be handled. Sometimes the profile is the proof that inlining is appropriate. A subroutine whose execution is as short as a few dozen ticks can be measured meaningfully using an automated tool based on perfctr.