On Tue, 10 Jun 2014 14:17:54 +0900
Namhyung Kim <namhy...@gmail.com> wrote:
> Hi Steve,
>
> On Fri, 06 Jun 2014 12:30:37 -0400, Steven Rostedt wrote:
> > From: "Steven Rostedt (Red Hat)" <rost...@goodmis.org>
> >
> > When calculating the average and standard deviation, it is required that
> > the count be less than UINT_MAX, otherwise the do_div() will get
> > undefined results. After 2^32 counts of data, the average and standard
> > deviation should pretty much be set anyway.
>
> [SNIP]
> > if (bm_cnt > 1) {
> > /*
> > * Apply Welford's method to calculate standard deviation:
> > * s^2 = 1 / (n * (n-1)) * (n * \Sum (x_i)^2 - (\Sum x_i)^2)
> > */
> > stddev = (u64)bm_cnt * bm_totalsq - bm_total * bm_total;
> > - do_div(stddev, bm_cnt);
> > - do_div(stddev, bm_cnt - 1);
> > + do_div(stddev, (u32)bm_cnt);
> > + do_div(stddev, (u32)bm_cnt - 1);
> > } else
> > stddev = 0;
>
> I also think that this if-else can go as it checks bm_cnt == 1 above.
>
I noticed this too, but just to keep gcc from complaining, I left it in.
-- Steve
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