From: "Doug Smythies" <dsmythies@telus.net>
To: "'Stratos Karafotis'" <stratosk@semaphore.gr>
Cc: <linux-pm@vger.kernel.org>, <linux-kernel@vger.kernel.org>,
        <rjw@rjwysocki.net>, <viresh.kumar@linaro.org>,
        <dirk.j.brandewie@intel.com>
References: <1402490012-19969-1-git-send-email-stratosk@semaphore.gr> <009b01cf857a$d5032090$7f0961b0$@net> <539862DB.9060905@semaphore.gr>
In-Reply-To: <539862DB.9060905@semaphore.gr>
Subject: RE: [PATCH] cpufreq: intel_pstate: Fix rounding of core_pct
Date: Wed, 11 Jun 2014 08:02:19 -0700
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On 2104.06.11 07:08 Stratos Karafotis wrote:
> On 11/06/2014 04:41 μμ, Doug Smythies wrote:
> 
> No.
> 
> The intent was only ever to round properly the pseudo floating point result of the divide.
> It was much more important (ugh, well 4 times more) when FRACBITS was still 6, which also got changed to 8 in a recent patch.
> 

Are you sure?

Yes.

> This rounding was very recently added.
> As far as I can understand, I don't see the meaning of this rounding, as is.
> Even if FRAC_BITS was 6, I think it would have almost no improvement in
> calculations.

Note: I had not seen this e-mail when I wrote a few minutes ago:

You may be correct.
If Dirk agrees, I will re-analyse the entire driver for rounding effects soon.
When FRACBITS was 6 there were subtle cases where the driver would get stuck, and not make a final pstate change, with the default PID gains.
Other things have changed, and the analysis needs to be re-done.

... Doug


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