Yo Hal! On Wed, 01 Mar 2017 15:24:08 -0800 Hal Murray <hmur...@megapathdsl.net> wrote:
> RFC1589 describes an in-kernel PLL that synchronizes the system clock to an > external PPS signal. RFC1589 is what the kernel did in 1995. Mills had input to an update to the in kernel PLL in 1999. I have no idea about any changes after that. A quick search of git log showed no changes there for a while. > Some/many OSes/distros don't ship a kernel that supports the > in-kernel PLL. In particular, it isn't available in Linux when > compiled with NO_HZ. I think that is an implementation detail rather > than anything fundamental. NO_HZ saves power on idle systems. It's > important for battery life on laptops. NO_HZ is gone in Linux 4.10. If is sort of replaced by CONFIG_NO_HZ_IDLE CONFIG_NO_HZ=y is the default in all in tree defconfig's. > I think it is likely that we would get results similar to the > in-kernel PLL if we copied the code to user-land and called it as > soon as the PPS data was available. Would be an interesting check. The code is in kernel/time/time.c > We should work on a NO_HZ version of ntpd. ntpd works just fine with NO_HZ_IDLE. I'm not sure how it exactly compares to the other 2 options; NO_HZ_FULL and HZ_PERIODIC. But I agree it could be better at power awareness. RGDS GARY --------------------------------------------------------------------------- Gary E. Miller Rellim 109 NW Wilmington Ave., Suite E, Bend, OR 97703 g...@rellim.com Tel:+1 541 382 8588 Veritas liberabit vos. -- Quid est veritas? "If you can’t measure it, you can’t improve it." - Lord Kelvin
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