Achim Gratz Stromeko at nexgo.de
Sun Apr 14 20:25:34 UTC 2019

Hal Murray via devel writes:
> devel at ntpsec.org said:
>> That's a fantastically wierd distribution.  Here's what my old single core
>> Athlon64 does: 
> Your sample is what I would expect from a system that isn't doing much.  If 
> there is other activity going on, the clean bell curve gets spread out due to 
> cache reloads and such.

HPET is a travel out to ACPI system registers mapped into memory, this
should never be never cached.  That's why HPET is really slow to read,
but it should be fairly consistent.  I've just tested it with (more)
load and the histogram stayed essentially the same.  It's only a single
core of course.

Here's what my (unloaded) Haswell does via TSC:

--8<---------------cut here---------------start------------->8---
ntpsec/attic> ./clocks
      res   avg     min  dups  CLOCK
        1    22      12        CLOCK_REALTIME
  4000000     4 4000058    -2  CLOCK_REALTIME_COARSE
        1    16      12        CLOCK_MONOTONIC
        1   242     232        CLOCK_MONOTONIC_RAW
        1   241     232        CLOCK_BOOTTIME

Histogram: CLOCK_REALTIME, 5 ns per bucket, 1000000 samples.
        ns      hits
        12    799739
        17    200210
        22         2
        27         2
        57         1
46 samples were bigger than 62.
--8<---------------cut here---------------end--------------->8---

That also doesn't change much with load.

+<[Q+ Matrix-12 WAVE#46+305 Neuron microQkb Andromeda XTk Blofeld]>+

SD adaptation for Waldorf Blofeld V1.15B11:

More information about the devel mailing list