On Mon, Jan 23, 2017 at 08:44:53PM +0100, Paolo Bonzini wrote: > If you just implement getclock64 the PTP_SYS_OFFSET output: > > device clock | |sample2| |sample4| |sample6| ... > ------------------------------------------------------------- > realtime clock |sample1| |sample3| |sample5| > > has a very large distance between samples on the same line (about 1 us), > and I think it is too noisy for userspace to make sense of the output. One microsecond is not too bad at all. The PCIe devices have intervals of 5-6 usec, and the result is quite usable, certainly better than generic NTP. > Marcelo's patch then produces fake realtime clock samples that, however, > let chrony derive the cross timestamps that KVM produced in the first > place. The outcome is really great accuracy compared to previous > versions of the patch, often just +/- 2 or 3 nanoseconds. Why can't chrony learn about PTP_SYS_OFFSET_PRECISE? Thanks, Richard
