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

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Message-ID: <f488382f0910070124v6f1e1539gbeb7765ab6f32231@mail.gmail.com>
Date:	Wed, 7 Oct 2009 01:24:13 -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 1:14 AM, Eero Nurkkala
<ext-eero.nurkkala@...ia.com> wrote:
> On Wed, 2009-10-07 at 10:05 +0200, ext Steven Noonan wrote:
>> > 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
>> >
>> >
>
> <------------Sidenote------------------------------>
> Vankatesh, I think the following is not smp friendly:
>        cpufreq_conservative.c:
>        /* Get Absolute Load */
>        for_each_cpu(j, policy->cpus) {
>        ...
>        load = 100 * (wall_time - idle_time) / wall_time;
>
>        now the load is only considered from the last cpu in line?
>        in ondemand, load goes to max_load_freq...so max is taken
>        from all cpus out there. (well, doesn't seem like the case with
>        conservative). Of course I may be wrong, and things are like
>        supposed.
> </------------Sidenote------------------------------>
>
> Steven, how do the cpu loads look like without the patch?

They're sane:

[   40.019381] cpufreq load = 100 * (66666 - 66337) / 66666 = 0
[   40.019396] cpufreq load = 100 * (66666 - 66299) / 66666 = 0
[   73.352580] cpufreq load = 100 * (66717 - 66349) / 66717 = 0
[   73.352595] cpufreq load = 100 * (66634 - 63848) / 66634 = 4
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