From 5ad79d9b2037c0676aab1c92f9f6ac7fb77c9a97 Mon Sep 17 00:00:00 2001 From: Andriy Gapon Date: Fri, 14 Apr 2017 15:31:04 +0000 Subject: [PATCH] dtrace: fix normalization of stddev aggregation To be upstreamed. Discussed with: Bryan Cantrill MFC after: 2 weeks Sponsored by: Panzura --- cddl/contrib/opensolaris/lib/libdtrace/common/dt_consume.c | 2 ++ 1 file changed, 2 insertions(+) diff --git a/cddl/contrib/opensolaris/lib/libdtrace/common/dt_consume.c b/cddl/contrib/opensolaris/lib/libdtrace/common/dt_consume.c index de574a330268..62c120388b18 100644 --- a/cddl/contrib/opensolaris/lib/libdtrace/common/dt_consume.c +++ b/cddl/contrib/opensolaris/lib/libdtrace/common/dt_consume.c @@ -389,8 +389,10 @@ dt_stddev(uint64_t *data, uint64_t normal) * 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];