On Wed, May 17, 2017 at 9:13 AM, Miroslav Lichvar <mlich...@redhat.com> wrote: > This is an attempt to improve stability and accuracy of the system clock > with very accurate time sources like the new PTP KVM clock or NTP/PTP > using hardware timestamping. It affects mainly kernels running with > NOHZ. It requires updating of the old ia64 and powerpc vsyscalls. > > The main problem is that the error accumulated in the ntp_error register > takes too long to correct and this cannot be easily fixed. There are > four sources of the error: > - rounding of time for old vsyscalls > - alignment of frequency adjustments to ticks > - iterative correction of the multiplier > - limited resolution of the multipler > > Instead of trying to correct the error faster, the patches remove the > first three sources. With the only remaining source the correction logic > can be simplified and the frequency of the clock is much more stable and > accurate. > > Simulations of a frequency step in linux-tktest (values are in ppm and > nanoseconds):
So thanks for sending these out. I still need to look them over in depth, but can I make another ask here? :) Could you submit your linux-tktest infrastructure to the kselftests dir? It would be really nice for folks to be able to reproduce your results be able to do similar testing for regressions. thanks -john
