Yo Hal! On Tue, 08 Jan 2019 04:06:57 -0800 Hal Murray via devel <devel@ntpsec.org> wrote:
> It gets built by default, so all you have to do is run
> ./build/main/attic/clocks
I have been thinking in a similar vein. When my PPS is more accurate
than the granularity of the system clock odd things are happening.
Also idd that the results are so different for clocks than in gpsd with
the clock_test program.
All the hosts below have the CPU governor set to performance.
For example, on an E3-1245 v3 @ 3.40GHz:
# ./clocks
res avg min dups CLOCK
1 15 11 CLOCK_REALTIME
10000000 4 999999999 0 CLOCK_REALTIME_COARSE
1 15 11 CLOCK_MONOTONIC
1 204 192 CLOCK_MONOTONIC_RAW
1 206 200 CLOCK_BOOTTIME
Histogram: CLOCK_REALTIME, 5 ns per bucket, 1000000 samples.
ns hits
11 713555
16 286093
21 314
26 18
31 4
16 samples were bigger than 36.
# ./clock_test
samples 101, delay 10000000 ns
min 51 ns, max 74 ns, mean 53 ns, median 52 ns, StdDev 3 ns
clocks seems to show a clock granularity of 11 ns, but clock_test shows 51 ns.
On an E5-1620 v3 @ 3.50GHz
# ./clocks
res avg min dups CLOCK
1 23 16 CLOCK_REALTIME
3333333 9 3333330 -2 CLOCK_REALTIME_COARSE
1 22 16 CLOCK_MONOTONIC
1 301 214 CLOCK_MONOTONIC_RAW
1 311 214 CLOCK_BOOTTIME
Histogram: CLOCK_REALTIME, 5 ns per bucket, 1000000 samples.
ns hits
16 10746
21 3894
26 246
31 2
36 2
46 1
56 13
66 1
76 1
81 3
91 3
96 1
101 1
121 1
126 5
131 1
136 1
141 2
151 1
156 2
186 1
351 1
985071 samples were bigger than 1266.
# ./clock_test
samples 101, delay 10000000 ns
min 24 ns, max 297 ns, mean 53 ns, median 48 ns, StdDev 34 ns
clocks shows a granularity of 16 ns, but clock_test shows 24 ns.
And on a RasPi 3B whith 32 bit kernel:
# ./clock
res avg min dups CLOCK
1 301 260 CLOCK_REALTIME
1000000 182 999993 -158 CLOCK_REALTIME_COARSE
1 289 260 CLOCK_MONOTONIC
1 1035 989 CLOCK_MONOTONIC_RAW
1 1442 1354 CLOCK_BOOTTIME
Histogram: CLOCK_REALTIME, 5 ns per bucket, 1000000 samples.
ns hits
260 492820
310 506652
360 30
365 51
415 66
381 samples were bigger than 420.
# ./clock_test
samples 101, delay 10000000 ns
min 260 ns, max 989 ns, mean 353 ns, median 364 ns, StdDev 71 ns
And here the two tests seem to agree...
RGDS
GARY
---------------------------------------------------------------------------
Gary E. Miller Rellim 109 NW Wilmington Ave., Suite E, Bend, OR 97703
g...@rellim.com Tel:+1 541 382 8588
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"If you can’t measure it, you can’t improve it." - Lord Kelvin
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