linux-kernel - RE: [PATCH] cpufreq: intel_pstate: Fix rounding of core

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Message-ID: <00a001cf8586$24eb5c70$6ec21550$@net>
Date:	Wed, 11 Jun 2014 08:02:19 -0700
From:	"Doug Smythies" <dsmythies@...us.net>
To:	"'Stratos Karafotis'" <stratosk@...aphore.gr>
Cc:	<linux-pm@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
	<rjw@...ysocki.net>, <viresh.kumar@...aro.org>,
	<dirk.j.brandewie@...el.com>
Subject: RE: [PATCH] cpufreq: intel_pstate: Fix rounding of core_pct


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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