On Tue, 18 Sep 2018, Thomas Gleixner wrote: > On Tue, 18 Sep 2018, Thomas Gleixner wrote: > > On Tue, 18 Sep 2018, Peter Zijlstra wrote: > > > > Your memory serves you right. That's indeed observable on CPUs which > > > > lack TSC_ADJUST. > > > > > > But, if the gtod code can observe this, then why doesn't the code that > > > checks the sync? > > > > Because it depends where the involved CPUs are in the topology. The sync > > code might just run on the same package an simply not see it. Yes, w/o > > TSC_ADJUST the TSC sync code can just fail to see the havoc. > > Even with TSC adjust the TSC can be slightly off by design on multi-socket > systems. Here are the gory details: https://lore.kernel.org/lkml/3c1737210708230408i7a8049a9m5db49e6c4d89ab62@xxxxxxxxxxxxxx/ The changelog has an explanation as well. d8bb6f4c1670 ("x86: tsc prevent time going backwards") I still have one of the machines which is affected by this. Thanks, tglx _______________________________________________ devel mailing list devel@xxxxxxxxxxxxxxxxxxxxxx http://driverdev.linuxdriverproject.org/mailman/listinfo/driverdev-devel
