Achim Gratz writes:
> Eric S. Raymond writes:
>> I'd take a patch to fix this.
>
> Can do if you tell me where's the source repository.
Nevermind, I found it.
>From 71af21049fcc58711c55a815e4028a11a75a4929 Mon Sep 17 00:00:00 2001
From: Achim Gratz <strom...@stromeko.de>
Date: Sun, 29 Jan 2017 19:46:42 +0100
Subject: [PATCH 1/2] correct tickless kernel explanation
---
index.txt | 15 +++++++++++----
1 file changed, 11 insertions(+), 4 deletions(-)
diff --git a/index.txt b/index.txt
index 8000d96..7f2c0c8 100644
--- a/index.txt
+++ b/index.txt
@@ -613,10 +613,17 @@ the others are missing, your setup will probably not work.
== Optimize system performance ==
-An optimization that is convenient to apply at this point is telling
-the kernel to run tickless (see <<TICKLESS>> for technical detaills).
-This can seriously reduce the jitter and offset in a GPS PPS time
-server.
+Modern Linux kernels stop the scheduler timing interrupt (also known
+as tick) when the last core of the processor goes idle since in the
+absence of a non-scheduler triggered interrupt there won't be anything
+to schedule on the next tick (this is called a "tickless kernel", see
+<<TICKLESS>> for technical details). This helps to conserve power by
+keeping the CPU and the rest of the system in deeper sleep states for
+longer. However, NTP was designed with the assumption of a tick
+interrupt and therefore the jitter and offset in a GPS PPS based time
+server can seriously degrade if it's not present. In order to avoid
+this degradation, we need to tell the kernel to keep the tick running
+even when the system would otherwise be completely idle.
{--config} On the Pi, add this to the end of the kernel command-line in
/boot/cmdline.txt:
--
2.11.0
>From 71fd57562f4862b35ca5122077f01fc4554b096e Mon Sep 17 00:00:00 2001
From: Achim Gratz <strom...@stromeko.de>
Date: Sun, 29 Jan 2017 19:47:47 +0100
Subject: [PATCH 2/2] mention availability of the "conservative" performance
governor
---
index.txt | 5 +++++
1 file changed, 5 insertions(+)
diff --git a/index.txt b/index.txt
index 7f2c0c8..a922562 100644
--- a/index.txt
+++ b/index.txt
@@ -648,6 +648,11 @@ You can verify with the following command, which should print
$ cat /sys/devices/system/cpu/cpu*/cpufreq/scaling_governor
------------------------------------------------------------------------
+If you want to run the system constantly at the lowest frequency
+instead (maybe to avoid thermal problems) you can use the governor
+"conservative". Everything will run slower than with governor
+"performance", but consistently so and the system will stay cooler.
+
== Smoke-test the GPS/HAT combination ==
To test that you can read data from the device, do this:
--
2.11.0
Regards,
Achim.
--
+<[Q+ Matrix-12 WAVE#46+305 Neuron microQkb Andromeda XTk Blofeld]>+
Factory and User Sound Singles for Waldorf rackAttack:
http://Synth.Stromeko.net/Downloads.html#WaldorfSounds
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