On Thu, Oct 15, 2020 at 07:52:06AM +0200, Juergen Perlinger wrote: > Another thing that gets into the way are the energy saving strategies > modern CPUs employ, like reducing the clock speed and distribute load > over cores. So unless you nail down the IRQ to a certain core and > prevent cores from going to full sleep, the interrupt rescheduling can > add another few usecs. IRQ processing was never a high speed thing on > x86 platforms to start with, and it never kept up with speed boost all > other parts of the architecture got, AFAIK.
Setting the CPU to a fixed frequency (e.g. using the userspace governor) can help a lot with the stability of timestamping, not just of the PPS signal, but also received NTP packets. > In short, your numbers look familiar, and I don't know how to improve > the much without dedicated hardware. I'm dreaming of some FPGA hardware > on a PCIe board at an affordable price... Not an FPGA, but the Intel I210 costs about $50 and it has a nice hardware clock with PPS input/output, which is well supported in Linux. It's a NIC, so you can use the same clock for timestamping PPS and NTP packets, avoiding any asymmetries on the PCIe bus between the PPS-timestamping hardware, CPU, and the NIC, which allows you to make an NTP server accurate to few tens of nanoseconds. -- Miroslav Lichvar _______________________________________________ questions mailing list [email protected] http://lists.ntp.org/listinfo/questions
