On Fri, 2015-11-06 at 17:57 +0100, Hans Petter Selasky wrote: > On 11/06/15 17:51, Hans Petter Selasky wrote: > > On 11/06/15 17:43, Ian Lepore wrote: > > > On Fri, 2015-11-06 at 17:28 +0100, Hans Petter Selasky wrote: > > > > Hi, > > > > > > > > Do the test II results change with this setting? > > > > > > sysctl kern.timecounter.alloweddeviation=0 > > > > > > > Yes, it looks much better: > > > > debug.total: 10013 -> 0 > > debug.total: 10013 -> 0 > > debug.total: 10012 -> 0 > > debug.total: 10012 -> 0 > > debug.total: 10012 -> 0 > > debug.total: 10013 -> 0 > > debug.total: 10012 -> 1 > > debug.total: 10013 -> 0 > > debug.total: 10013 -> 0 > > debug.total: 10013 -> 0 > > debug.total: 10012 -> 0 > > debug.total: 10013 -> 0 > > debug.total: 10013 -> 0 > > > > --HPS > > > > Thought I still see some unexpected dips, as the test runs for a > longer > amount of time. Not sure what the cause might be. > > > debug.total: 10013 -> 0 > > debug.total: 10013 -> 0 > > debug.total: 10013 -> 0 > > debug.total: 9844 -> 0 > > debug.total: 10013 -> 0 > > debug.total: 10013 -> 0 > > debug.total: 10012 -> 0 > > --HPS Is it possible your machine is occasionally falling into a deeper sleep state (C3 or whatever)? I think it can take hundreds of microseconds to wake up from some of the deeper power-saving modes. If not power-saving, just plain old system-is-busy could lead to the reduced counts occasionally, since each callout is scheduled as a delta from the current actual wakeup time, not a delta from the current scheduled wakeup time (i.e., there is a phase shift in the firing of events over time). Raising the priority of the test thread into the realtime range might help with system-busy variation. It's also a bit iffy that you're using eventtimers to measure the performance of eventtimers (by using sleep 1 in the script). That explains the +12/13 count every second, not the reduced counts unless we speculate that sleep is returning early (which I have NEVER caught it doing). If you have a PPS source available, that can make a good way to sleep based on an off-box timing signal and avoid using a clock to measure itself. But I doubt it would make a big difference in this case. -- IanReceived on Fri Nov 06 2015 - 16:23:08 UTC
This archive was generated by hypermail 2.4.0 : Wed May 19 2021 - 11:41:00 UTC