From: Steven Rostedt <rostedt@goodmis.org>
To: Matthias Schiffer <mschiffer@universe-factory.net>
Cc: mingo@redhat.com, linux-kernel@vger.kernel.org
Subject: Re: [PATCH] ftrace: fix stddev calculation in function profiler (again)
Date: Mon, 26 Mar 2018 12:51:31 -0400 [thread overview]
Message-ID: <20180326125131.15fba249@gandalf.local.home> (raw)
In-Reply-To: <f208c5c360f1e86327b0adbb879d61f4779e8ddd.1521908409.git.mschiffer@universe-factory.net>
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:
next prev parent reply other threads:[~2018-03-26 16:51 UTC|newest]
Thread overview: 7+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-03-24 16:26 Matthias Schiffer
2018-03-24 22:03 ` Matthias Schiffer
2018-03-25 17:09 ` Matthias Schiffer
2018-03-26 16:59 ` Steven Rostedt
2018-03-26 16:51 ` Steven Rostedt [this message]
2018-03-27 14:51 ` Matthias Schiffer
2018-03-27 15:14 ` Steven Rostedt
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