Re: [Ntp] Antw: Re: Antw: [EXT] Minutes from IETF 108 NTP WG session

Miroslav Lichvar <mlichvar@redhat.com> Mon, 03 August 2020 11:21 UTC

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Date: Mon, 03 Aug 2020 13:21:30 +0200
From: Miroslav Lichvar <mlichvar@redhat.com>
To: Ulrich Windl <Ulrich.Windl@rz.uni-regensburg.de>
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Subject: Re: [Ntp] Antw: Re: Antw: [EXT] Minutes from IETF 108 NTP WG session
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On Mon, Aug 03, 2020 at 01:01:02PM +0200, Ulrich Windl wrote:
> On one machine I got these debugging messages:
> (D)get_res: resolution is 0.000000001 ## from POSIX call
> (D)get_res: smallest delta is 0.000001514
> (D)get_res: largest delta is 0.000001695
> (I)set_resolution: ts 0.000001514, digits 6, nsecs 1000

This suggests the system is not using the TSC clocksource, but
something slower like HPET. Check the following files:

/sys/devices/system/clocksource/clocksource0/current_clocksource
/sys/devices/system/clocksource/clocksource0/available_clocksource

> So your machines must be way faster... OK, I tried the latest generation we
> have:

No, they are not faster, just using the TSC clocksource. On some
machines it's unreliable, so the kernel may need to switch to a slower
clocksource. IIRC even the first Intel Core and AMD Athlon 64 CPUs
from the 2000s were about 50ns or better. Make sure the CPU is running
at full speed (e.g. disabled ondemand governor).

-- 
Miroslav Lichvar