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

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Date:	Wed, 07 Oct 2009 11:14:23 +0300
From:	Eero Nurkkala <ext-eero.nurkkala@...ia.com>
To:	ext Steven Noonan <steven@...inklabs.net>
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, 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?

- Eero



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