linux-kernel - Re: [RFC v3 0/5] cpufreq:LAB: Support for LAB governor.

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Message-ID: <CAKohpokz9SknhPH_sgGE6Q8DB+QtaJKSwMG4WgfmWet9skMKUA@mail.gmail.com>
Date:	Tue, 18 Mar 2014 12:25:06 +0530
From:	Viresh Kumar <viresh.kumar@...aro.org>
To:	Lukasz Majewski <l.majewski@...sung.com>
Cc:	"Rafael J. Wysocki" <rjw@...ysocki.net>,
	"cpufreq@...r.kernel.org" <cpufreq@...r.kernel.org>,
	Linux PM list <linux-pm@...r.kernel.org>,
	Jonghwa Lee <jonghwa3.lee@...sung.com>,
	Lukasz Majewski <l.majewski@...ess.pl>,
	linux-kernel <linux-kernel@...r.kernel.org>,
	Bartlomiej Zolnierkiewicz <b.zolnierkie@...sung.com>,
	Myungjoo Ham <myungjoo.ham@...sung.com>,
	Tomasz Figa <t.figa@...sung.com>,
	Thomas Abraham <ta.omasab@...il.com>,
	Thomas Abraham <thomas.ab@...sung.com>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	linux-samsung-soc <linux-samsung-soc@...r.kernel.org>,
	Lists linaro-kernel <linaro-kernel@...ts.linaro.org>
Subject: Re: [RFC v3 0/5] cpufreq:LAB: Support for LAB governor.

On 17 March 2014 21:08, Lukasz Majewski <l.majewski@...sung.com> wrote:
>> Despite this patch set is working and applicable on top of 3.14-rc5,
>> please regard it solely as a pure RFC.
>>
>> This patch provides support for LAB governor build on top of ondemand.
>> Previous version of LAB can be found here:
>> http://thread.gmane.org/gmane.linux.kernel/1484746/match=cpufreq
>>
>> LAB short reminder:
>>
>> LAB uses information about how many cores are in "idle" state (the
>> core idleness is represented as the value between 0 and 100) and the
>> overall load of the system (from 0 to 100) to decide about frequency
>> to be set. It is extremely useful with SoCs like Exynos4412, which
>> can set only one frequency for all cores.
>>
>> Important design decisions:
>>
>> - Reuse well established ondemand governor's internal code. To do this
>>   I had to expose some previously static internal ondemand code.
>>   This allowed smaller LAB code when compared to previous version.
>>
>> - LAB works on top of ondemand, which means that one via device tree
>>   attributes can specify if and when e.g. BOOST shall be enabled or
>> if any particular frequency shall be imposed. For situation NOT
>> important from the power consumption reduction viewpoint the ondemand
>> is used to set proper frequency.
>>
>> - It is only possible to either compile in or not the LAB into the
>> kernel. There is no "M" option for Kconfig. It is done on purpose,
>> since ondemand itself can be also compiled as a module and then it
>> would be possible to remove ondemand when LAB is working on top of it.
>>
>> - The LAB operation is specified (and thereof extendable) via device
>> tree lab-ctrl-freq attribute defined at /cpus/cpu0.
>>
>>
>> Problems:
>> - How the governor will work for big.LITTLE systems (especially
>> Global Task Scheduling).
>> - Will there be agreement to expose internal ondemand code to be
>> reused for more specialized governors.
>>
>> Test HW:
>>       Exynos4412 - Trats2 board.
>> Above patches were posted on top of Linux 3.14-rc5
>> (SHA1: 3f9590c281c66162bf8ae9b7b2d987f0a89043c6)
>>
>
> Any comments about those patches?

Sorry for being late on reviewing these..

I tried to go through the patches but didn't looked at the minutest
of the details. Its been a long time when you first sent this patchset.
And the memories have corrupted by now :) ..

To get context back, can we discuss again the fundamentals behind
this new governor you are proposing. And then we can discuss about
it again, its pros/cons, etc..

I tried to go to earlier threads but I think we better do it again..

People are reluctant in getting another governor in and want to give
existing governors a try if possible.

So, please explain the basics behind your governor again and then
we can put our arguments again..

--
viresh
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