| Re: [chrony-dev] Nanosecond timestamps |
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On Mon, Nov 07, 2016 at 03:04:50PM -0800, Denny Page wrote:
> > On Nov 07, 2016, at 05:00, Miroslav Lichvar <mlichvar@xxxxxxxxxx> wrote:
> > What HW and kernel do you use?
....
> The two units under test, 192.168.230.240 and 192.168.230.244, were LeoNTP units: http://leontp.com <http://leontp.com/>. The Leo does not have an OS per se, but implements NTP as dedicated hardware/firmware. Very, very consistent.
Thanks for the details. Very interesting.
On Tue, Nov 08, 2016 at 01:23:35AM -0800, Denny Page wrote:
> CONFIG_NO_HZ_IDLE=y
> CONFIG_HIGH_RES_TIMERS=y
> # CONFIG_MODULES is not set
> CONFIG_DEFAULT_CFQ=y
> CONFIG_NR_CPUS=<SET TO ACTUAL NUMBER>
> # CONFIG_SCHED_SMT is not set
> CONFIG_SCHED_MC=y
> CONFIG_PREEMPT=y
> CONFIG_HZ_1000=y
> # CONFIG_PM is not set
> CONFIG_ACPI=y
> # CONFIG_CPU_FREQ is not set
> # CONFIG_CPU_IDLE is not set
> CONFIG_HPET=y
>
> There is always room for improvement, so feedback is welcome.
I'm wondering if we should be collecting these tips and put them on
the web or in the manual pages.
In my experience disabling NO_HZ (e.g. nohz=off on kernel command
line) can help a bit. With older kernels it used to be a lot, but
there were some improvements in the kernel and the difference is much
smaller now.
> In addition to the kernel, I disable eee and interrupt coalescing on the network interfaces.
Oh, I knew ethernet has some power saving features, but I didn't
realize they could increase latency/jitter. I'll need to experiment
with this :).
As for interrupt coalescing, it can help significantly with some
cards, but on some (e.g. i210) it seems to be adaptive and changing
the values didn't do much the last time I experimented with it. I
didn't figure out how to disable it completely.
--
Miroslav Lichvar
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