Hal Murray via devel writes:
> devel@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.
Regards,
Achim.
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