On Wed, Jul 23, 2014 at 02:36:24AM +0000, Dylan Davis wrote: > I was experimenting to see how far I could push PTP accuracy using software > timstamps. I have a simple test setup with a single master and a single slave, > configured to use the P2P delay mechanism. logSyncInterval on the master is > set > to -8.
-8 is an extremenly short update interval, I'm a bit surprised it still works. Did you use the default PI configuration? > Both systems have tickless kernel disabled (nohz=off). With both systems > idle I can reach around 2us rms offset and 15-20us peak offset. If I then > fully > load all 4 cores of the slave (using the 'stress' program), after a brief > spike > the accuracy of the synchronization actually *improves*, reaching 300-500ns > rms > offset and around 3us peak offset. Removing the CPU load brings the offset > back > to its original magnitude. In both cases the rms and max offset values are > consistent, with only occasional spikes. Interestingly, the reported delay > under > load is 12us less than when unloaded. Beside what Richard has mentioned, I think it could be also the variability in the time it takes the CPU to wake up from various powersaving states. You can try setting the idle= or intel_idle.max_cstate= kernel options and see if that helps. -- Miroslav Lichvar ------------------------------------------------------------------------------ Want fast and easy access to all the code in your enterprise? Index and search up to 200,000 lines of code with a free copy of Black Duck Code Sight - the same software that powers the world's largest code search on Ohloh, the Black Duck Open Hub! Try it now. http://p.sf.net/sfu/bds _______________________________________________ Linuxptp-users mailing list [email protected] https://lists.sourceforge.net/lists/listinfo/linuxptp-users
