On Tue, Jan 24, 2017 at 06:32:43AM +0100, Richard Cochran wrote: > On Mon, Jan 23, 2017 at 09:06:20PM -0200, Marcelo Tosatti wrote: > > Can you please describe what problem exists with this scheme? > > This new kernel code exists just because chrony doesn't implement the > PRECISE ioctl. Instead of adding new "fake" modes, just teach chrony > about the better method. The latest development code of chrony now supports the PRECISE ioctl. I did some tests with an e1000e NIC (i219) and it seemed the stability was slightly worse than with the non-PRECISE ioctl, but there was a 400-500ns offset between the two, so it should be much more accurate (we finally have something that avoids the asymmetry on the PCI-e bus?). Configuring the refclock with a shorter dpoll should compensate for the decrease in stability. In any case, there is a "nocrossts" option to not use the PRECISE ioctl even if it's supported. -- Miroslav Lichvar
