On Wed, Apr 11, 2018 at 04:38:44PM -0700, Jesus Sanchez-Palencia wrote: > Just breaking this down a bit, yes, TAI is the network time base, and the NICs > PTP clock use that because PTP is (commonly) based on TAI. After the PHCs have > been synchronized over the network (e.g. with ptp4l), my understanding is that > if applications want to use the clockid_t CLOCK_TAI as a network clock > reference > it's required that something (i.e. phc2sys) is synchronizing the PHCs and the > system clock, and also that something calls adjtime to apply the TAI vs UTC > offset to CLOCK_TAI.
Yes. I haven't seen any distro that sets the TAI-UTC offset after boot, nor are there any user space tools for this. The kernel is ready, though. > I was thinking about the full offload use-cases, thus when no scheduling is > happening inside the qdiscs. Applications could just read the time from the > PHC > clocks directly without having to rely on any of the above. On this case, > userspace would use DYNAMIC_CLOCK just to flag that this is the case, but I > must > admit it's not clear to me how common of a use-case that is, or even if it > makes > sense. 1588 allows only two timescales, TAI and ARB-itrary. Although it doesn't make too much sense to use ARB, still people will do strange things. Probably some people use UTC. I am not advocating supporting alternate timescales, just pointing out the possibility. Thanks, Richard
