linux-kernel - Re: [BISECTED] "conservative" cpufreq governor broken

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Message-ID: <f488382f0910070105g19cbf75ci8034f2917b7e5606@mail.gmail.com>
Date:	Wed, 7 Oct 2009 01:05:36 -0700
From:	Steven Noonan <steven@...inklabs.net>
To:	ext-eero.nurkkala@...ia.com
Cc:	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Rik van Riel <riel@...hat.com>,
	Venkatesh Pallipadi <venkatesh.pallipadi@...el.com>
Subject: Re: [BISECTED] "conservative" cpufreq governor broken

On Wed, Oct 7, 2009 at 12:49 AM, Eero Nurkkala
<ext-eero.nurkkala@...ia.com> wrote:
> On Wed, 2009-10-07 at 09:30 +0200, ext Steven Noonan wrote:
>>
>> Okay, wow, I'm a moron. I misread what cpu_idle() was intended to be
>> for. I thought that cpu_idle() was a function that was periodically
>> called whenever the CPU had nothing to do, but now I see that it's
>> actually the main loop. I should really read the code next time.
>>
>> I've moved the statistics printout code to the _inside_ of that
>> infinite loop and retested. I had it print every several hundred
>> iterations. Here's the results (note the machine was idle the whole
>> time, except for about the first 10-20 seconds while the machine
>> booted):
>>
>> [    3.627716] timings[0]: 2250511125 / 3627716116
>> [    6.946216] timings[0]: 4780901366 / 6946213531
>> [   13.355182] timings[0]: 9385417604 / 13355183525
>> [   18.551304] timings[1]: 16300853077 / 18551301189
>> [   21.589039] timings[0]: 15984495433 / 21589037480
>> [   47.152733] timings[1]: 44386121538 / 47152731476
>> [   51.682630] timings[0]: 45713834076 / 51682628295
>> [   79.587359] timings[0]: 73524821916 / 79587356820
>> [   88.630110] timings[1]: 85324277596 / 88630109605
>> [   96.082386] timings[0]: 89691306072 / 96082384539
>>
>
> Those look good.
>
> Well, might as well then go for:
> /drivers/cpufreq/cpufreq_conservative.c
> dbs_check_cpu() ->
> load = 100 * (wall_time - idle_time) / wall_time; <- What is your load?

That's probably the problem...

[   40.632277] cpufreq load = 100 * (66667 - 3310) / 66667 = 95
[   40.698947] cpufreq load = 100 * (66661 - 3238) / 66661 = 95
[   73.965425] cpufreq load = 100 * (66667 - 12820) / 66667 = 80
[   74.032095] cpufreq load = 100 * (66661 - 1124) / 66661 = 98
[  107.298571] cpufreq load = 100 * (66666 - 13092) / 66666 = 80
[  107.365301] cpufreq load = 100 * (66722 - 3317) / 66722 = 95
[  140.631717] cpufreq load = 100 * (66666 - 3311) / 66666 = 95
[  140.698387] cpufreq load = 100 * (66662 - 3237) / 66662 = 95

idle_time is wrong.

> Let assume load is sane, look for (in dbs_check_cpu())
>        if (load < (dbs_tuners_ins.down_threshold - 10)) {
>
> whether it is taken ever...if not, what is your
> (dbs_tuners_ins.down_threshold - 10) ?
>
> - Eero
>
>
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