On 6/6/07 10:30, "Jan Beulich" <jbeulich@xxxxxxxxxx> wrote: >> If you have an ACPI PM timer in your system (and if you have SMM then your >> system is almost certainly modern enough to have one) then surely the >> problem is fixed for all practical purposes? The problem was overflow of a >> fixed-width platform counter. The PIT wraps every ~50ms, but the ACPI PM >> timer will wrap only every ~4s. It would be quite unreasonable for SMM to >> take the CPU away for multiple seconds, even as a one-time boot operation. > > No, I don't think the problem's gone with the PM timer - it is just much less > likely. Since you depend on the TSC (which must generally be assumed be > unsyncronized across CPUs) and on the error correction factor (which shows > non-zero values every few seconds), getting the interpolated times on two > CPUs out of sync is still possible, and given the way the time keeping code > works even being off by just a single nanosecond may be fatal. If the error across CPUS is +/- just a few microseconds at worst then having the clocksource clamp to no less than the last timestamp returned seems a reasonable fix. Time won't 'stop' for longer than the cross-CPU error, and that should always be a tiny value. -- Keir _______________________________________________ Virtualization mailing list Virtualization@xxxxxxxxxxxxxxxxxxxxxxxxxx https://lists.linux-foundation.org/mailman/listinfo/virtualization
