On Tue, 18 Sep 2018, Peter Zijlstra wrote: > On Tue, Sep 18, 2018 at 12:41:57PM +0200, Thomas Gleixner wrote: > > I still have one of the machines which is affected by this. > > Are we sure this isn't a load vs rdtsc reorder? Because if I look at the > current code: The load order of last vs. rdtsc does not matter at all. CPU0 CPU1 .... now0 = rdtsc_ordered(); ... tk->cycle_last = now0; gtod->seq++; gtod->cycle_last = tk->cycle_last; ... gtod->seq++; seq_begin(gtod->seq); now1 = rdtsc_ordered(); So if the TSC on CPU1 is slightly behind the TSC on CPU0 then now1 can be smaller than cycle_last. The TSC sync stuff does not catch the small delta for unknown raisins. I'll go and find that machine and test that again. Thanks, tglx _______________________________________________ devel mailing list devel@xxxxxxxxxxxxxxxxxxxxxx http://driverdev.linuxdriverproject.org/mailman/listinfo/driverdev-devel
