H. Peter Anvin wrote:
> I would like to see the error bars on your measurement.
I just ran it on my laptop 20 times in a row and it printed exactly the
same values every time:
Kernel reports clock frequency: 366.601 MHz
Measured clock frequency: 366.584 MHz
Well we need more precision than that. So here goes:
Kernel reports clock frequency: 366.601000 MHz
Measured clock frequency: 366.584116 MHz
Measured clock frequency: 366.584071 MHz
Measured clock frequency: 366.584108 MHz
Measured clock frequency: 366.584116 MHz
Measured clock frequency: 366.584090 MHz
Measured clock frequency: 366.583968 MHz
Measured clock frequency: 366.584069 MHz
Measured clock frequency: 366.584106 MHz
Measured clock frequency: 366.584172 MHz
Measured clock frequency: 366.584093 MHz
Measured clock frequency: 366.584077 MHz
Measured clock frequency: 366.583939 MHz
Measured clock frequency: 366.584083 MHz
Measured clock frequency: 366.584118 MHz
Measured clock frequency: 366.584062 MHz
Measured clock frequency: 366.584085 MHz
Measured clock frequency: 366.584066 MHz
Measured clock frequency: 366.610417 MHz <- anomaly :-)
Measured clock frequency: 366.584109 MHz
Measured clock frequency: 366.584062 MHz
Measured clock frequency: 366.582293 MHz
Measured clock frequency: 366.584103 MHz
Measured clock frequency: 366.584093 MHz
Measured clock frequency: 366.584107 MHz
Measured clock frequency: 366.584059 MHz
Measured clock frequency: 366.583985 MHz
Measured clock frequency: 366.584133 MHz
Measured clock frequency: 366.584092 MHz
Measured clock frequency: 366.584087 MHz
Measured clock frequency: 366.555754 MHz <- another deviant!
Measured clock frequency: 366.584044 MHz
Measured clock frequency: 366.584109 MHz
Measured clock frequency: 366.584084 MHz
Measured clock frequency: 366.583608 MHz
Measured clock frequency: 366.584112 MHz
Measured clock frequency: 366.584134 MHz
Measured clock frequency: 366.584049 MHz
Measured clock frequency: 366.584090 MHz
Measured clock frequency: 366.584155 MHz
Measured clock frequency: 366.584006 MHz
Measured clock frequency: 366.584182 MHz
Measured clock frequency: 366.584009 MHz
It takes the median of 1000 samples of the TSC time taken to do a
rdtsc/gettimeofday/rdtsc measurement, then uses that as the threshold
for deciding which of the subsequent 1000000 measurements are accepted.
Then linear regression through the accepted points.
I see a couple of results there which suggests a probable fault in the
filtering algorithm. Perhaps it should simply use the smallest TSC time
taken as the threshold.
Sorry, I'd need permission to post the code.
enjoy,
-- Jamie
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This archive was generated by hypermail 2b29 : Thu Mar 07 2002 - 21:01:13 EST