linux-kernel - Re: [PATCH] ftrace: print sample std dev when function profiling

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Date:	Tue, 27 Apr 2010 16:50:02 -0400
From:	Steven Rostedt <rostedt@...dmis.org>
To:	Chase Douglas <chase.douglas@...onical.com>
Cc:	linux-kernel@...r.kernel.org,
	Frederic Weisbecker <fweisbec@...il.com>,
	Ingo Molnar <mingo@...hat.com>
Subject: Re: [PATCH] ftrace: print sample std dev when function profiling

On Mon, 2010-04-26 at 14:02 -0400, Chase Douglas wrote:

> +	/* Sample standard deviation (s^2) */
> +	if (rec->counter <= 1)
> +		stddev = 0;
> +	else {
> +		stddev = rec->time_squared - rec->counter * avg * avg;
> +		do_div(stddev, (rec->counter - 1) * 1000); /* ns^2 -> us^2 */

Shouldn't this be:

	do_div(stddev, (rec->counter - 1) * 1000000); ?

(x / 1000)^2 == x^2 / 1000^2


-- Steve

> +	}
> +


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