From mboxrd@z Thu Jan  1 00:00:00 1970
From: "Doug Smythies" <dsmythies@telus.net>
Subject: RE: [PATCH] cpufreq, Fix overflow in busy_scaled due to long delay
Date: Thu, 11 Jun 2015 09:17:38 -0700
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To: 'Prarit Bhargava' <prarit@redhat.com>
Cc: "'Rafael J. Wysocki'" <rjw@rjwysocki.net>, linux-kernel@vger.kernel.org, 'Kristen Carlson Accardi' <kristen@linux.intel.com>, 'Viresh Kumar' <viresh.kumar@linaro.org>, linux-pm@vger.kernel.org


On 2015.06.11 08:01 Prarit Bhargava wrote:
> On 06/11/2015 10:51 AM, Doug Smythies wrote:
>> 
>> On 2015.06.10 16:46 Rafael J. Wysocki wrote:
>>> On Wednesday, June 10, 2015 09:18:45 AM Prarit Bhargava wrote:
>>>> I looked into switching to div64_s64() instead of the 32-bit version in
>>>> div_fp(), however, this would result in sample_ratio and core_busy returning
>>>> 0 which is something we don't want.
>> 
>> ???
>> Due to a great many overflow related issues, div_fp() was changed to div64_s64()
>> a long time ago.

> Doug,
>
> Nope -- in a linux.git tree (up-to-date as of 7:00AM ET this AM)
>
> static inline int32_t div_fp(int32_t x, int32_t y)
> {
>        return div_s64((int64_t)x << FRAC_BITS, y);
> }

> If we do want this to be div64_s64, I can make that change, however, I feel that
> a long delay like this should be ignored in the performance calculations in the
> driver and that's why I chose to go the direction I did.

Prarit,

Apologies to you and the list for the distraction. I mis-read "div_s64" as "div64_s64".
Your suggestion is a good one.

I do maintain that my point about the duration method being flawed is valid.
I proposed a fix for that some time ago.