Author: avg
Date: Wed May 24 11:11:13 2017
New Revision: 318784
URL: https://svnweb.freebsd.org/changeset/base/318784
Log:
MFC r316853: dtrace: fix normalization of stddev aggregation
Sponsored by: Panzura
Modified:
stable/10/cddl/contrib/opensolaris/lib/libdtrace/common/dt_consume.c
Directory Properties:
stable/10/ (props changed)
Modified: stable/10/cddl/contrib/opensolaris/lib/libdtrace/common/dt_consume.c
==============================================================================
--- stable/10/cddl/contrib/opensolaris/lib/libdtrace/common/dt_consume.c
Wed May 24 11:10:55 2017 (r318783)
+++ stable/10/cddl/contrib/opensolaris/lib/libdtrace/common/dt_consume.c
Wed May 24 11:11:13 2017 (r318784)
@@ -389,8 +389,10 @@ dt_stddev(uint64_t *data, uint64_t norma
* The standard approximation for standard deviation is
* sqrt(average(x**2) - average(x)**2), i.e. the square root
* of the average of the squares minus the square of the average.
+ * When normalizing, we should divide the sum of x**2 by normal**2.
*/
dt_divide_128(data + 2, normal, avg_of_squares);
+ dt_divide_128(avg_of_squares, normal, avg_of_squares);
dt_divide_128(avg_of_squares, data[0], avg_of_squares);
norm_avg = (int64_t)data[1] / (int64_t)normal / (int64_t)data[0];
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