stddev() Function

The value for the stddev() action is stored as a four-element array of 64-bit values. As with avg(), the first two values are a count of the individual data points and a sum of those data points. The lower two values contain a 128-bit representation of the sum of the squares of the individual data points. The third element contains the higher 64 bits of the value, and the fourth element contains the lower 64 bits. Standard deviation can be calculated as the square root of the average of the squares minus the square of the average: sqrt(average(x**2) - average(x)**2).

stddev() (dtrd_action == DTRACEAGG_STDDDEV)

Data Format for the stdev() Action