On Thu, Nov 20, 2014 at 07:27:47AM +0000, David Taylor wrote: > On 19/11/2014 11:56, Miroslav Lichvar wrote: > >Can you try 3.17 or later and see if it's fixed? Also, it would be > >interesting to know if adding nohz=off to the kernel command line > >instead of recompiling works as a workaround too. > > I found the right file (thanks, Rob, yes there are more options as you say) > and tried setting nohz=off but it made no difference - jitter still reported > as zero.
Interesting. When you tested the kernel compiled without CONFIG_NO_HZ, where ntpd reported non-zero jitter, was that the only difference compared to the original kernel which reported zero jitter? > How would I tell whether the nohz=off was actually accepted or not, i.e. how > to determine whether the kernel is tickless or not? I'm not sure if there is any reliable way to tell that from user-space, beside parsing the kernel command line. > pi@raspberrypi ~ $ cat /proc/interrupts | grep -i time > 3: 4351879 ARMCTRL BCM2708 Timer Tick > pi@raspberrypi ~ $ sleep 10 > pi@raspberrypi ~ $ cat /proc/interrupts | grep -i time > 3: 4353699 ARMCTRL BCM2708 Timer Tick > pi@raspberrypi ~ $ > > I don't know how to interpret the difference of 1820 in those two numbers. > The first two commands were typed by hand, by the way, the third with an > up-arrow recall. That's between 100 and 250 Hz, so the kernel could be compiled with CONFIG_HZ=100. Do you see that in the kernel config file? Does the interrupt rate change significantly when you load the CPU, e.g. by running "cat /dev/urandom > /dev/null" ? -- Miroslav Lichvar _______________________________________________ questions mailing list questions@lists.ntp.org http://lists.ntp.org/listinfo/questions