Hi Viresh,
Hi Viresh,
On 17 March 2014 21:08, Lukasz Majewski l.majewski@samsung.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 :) ..
Unfortunately memory is volatile ... since LAB governor is a follow up of BOOST, which review and inclusion took considerable time, some details could be forgotten.
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..
Please consider following links:
The original implementation - threads: http://thread.gmane.org/gmane.linux.power-management.general/32523/match=lab http://thread.gmane.org/gmane.linux.kernel/1484746/match=lab
LAB justification data: http://article.gmane.org/gmane.linux.kernel/1472381
People are reluctant in getting another governor in and want to give existing governors a try if possible.
As I've stated in the covering letter, this code is an extension of Ondemand.
This is totally different from what have been posted previously (v1, v2). The first LAB proposal was written with some parts copied from Ondemand. It was a separate, standalone governor.
The approach proposed in those patches is very different. It simply reuses Ondemand code as much as possible (timers, default attributes exported to sysfs, etc.).
On top of the Ondemand we have the LAB, which thereof is its optional extension. The existing code is reused and can be easily extracted as a common code.
So, please explain the basics behind your governor again and then we can put our arguments again..
I hope that provided overview is sufficient. More in depth information can be found in posted patches or provided LKML archives.
Viresh, will you find time for reviewing this RFC in a near future?
-- viresh