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SubjectRe: [PATCH] ftrace: fix stddev calculation in function profiler (again)
On Sat, 24 Mar 2018 17:26:38 +0100
Matthias Schiffer <mschiffer@universe-factory.net> wrote:

> @@ -905,8 +898,20 @@ static void profile_graph_return(struct ftrace_graph_ret *trace)
>
> rec = ftrace_find_profiled_func(stat, trace->func);
> if (rec) {
> + unsigned long long avg, delta1, delta2;
> +
> rec->time += calltime;
> - rec->time_squared += calltime * calltime;
> +
> + /* Apply Welford's method */
> + delta1 = calltime - rec->avg;
> +
> + avg = rec->time;
> + do_div(avg, rec->counter);

Can you find a way not to do a divide in every function call?

-- Steve

> + rec->avg = avg;
> +
> + delta2 = calltime - rec->avg;
> +
> + rec->stddev += delta1 * delta2;
> }
>
> out:

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