linux-kernel - Re: [PATCH 2/4] perf stat: Add computation of TopDown formulas

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Date:	Thu, 2 Jun 2016 06:56:51 -0500
From:	Nilay Vaish <nilayvaish@...il.com>
To:	Andi Kleen <ak@...ux.intel.com>
Cc:	Andi Kleen <andi@...stfloor.org>, acme@...nel.org,
	jolsa@...nel.org, Linux Kernel list <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 2/4] perf stat: Add computation of TopDown formulas

Andi,  I am talking about the if statement.  I don't know why it would
happen that nothing got measured.  I am guessing you saw it happen.
May be we can add a comment in the patch that it is possible that all
counter values are zero and therefore we need that if statement.

--
Nilay

On 1 June 2016 at 09:56, Andi Kleen <ak@...ux.intel.com> wrote:
> On Wed, Jun 01, 2016 at 09:50:07AM -0500, Nilay Vaish wrote:
>> On 24 May 2016 at 14:52, Andi Kleen <andi@...stfloor.org> wrote:
>> > +static double td_be_bound(int ctx, int cpu)
>> > +{
>> > +       double sum = (td_fe_bound(ctx, cpu) +
>> > +                     td_bad_spec(ctx, cpu) +
>> > +                     td_retiring(ctx, cpu));
>> > +       if (sum == 0)
>> > +               return 0;
>> > +       return sanitize_val(1.0 - sum);
>> > +}
>> > +
>>
>> Can you explain why we need the check on sum?
>
> You mean the if statement?
>
> Otherwise if nothing was measured it would always report everything backend bound,
> which wouldn't be correct.
>
> -Andi
>
> --
> ak@...ux.intel.com -- Speaking for myself only