Re: TEO as default governor ?

[Daniel Lezcano <daniel.lezcano@linaro.org>]

On 11/03/2025 19:26, Rafael J. Wysocki wrote:
> On Tue, Mar 11, 2025 at 7:00 PM Daniel Lezcano
> <daniel.lezcano@linaro.org> wrote:
>>
>> On 11/03/2025 18:34, Rafael J. Wysocki wrote:
>>> On Tue, Mar 11, 2025 at 5:47 PM Christian Loehle
>>> <christian.loehle@arm.com> wrote:
>>>>
>>>> On 3/11/25 16:31, Daniel Lezcano wrote:
>>>>>
>>>>> Hi,
>>>>>
>>>>> I think we can agree the teo governor is better then the menu governor.
>>>>>
>>>>> Would it make sense to make the teo governor the default governor ?
>>>>>
>>>>>
>>>>
>>>> Rafael's position seems to be quite conservative here.
>>>> Fact is menu is still the default on many systems.
>>>> Even worse, the really bad performance disadvantage when
>>>> using menu in an intercept-heavy workload has been fixed by Rafael :)
>>>> https://lore.kernel.org/lkml/bc7f915b-8d9f-4e05-9939-8b7ecc078f85@arm.com/
>>>>
>>>> FWIW I proposed this a while ago:
>>>> https://lore.kernel.org/lkml/20240905092645.2885200-3-christian.loehle@arm.com/
>>>
>>> It will help if one can make a really convincing case for this change
>>> (that is, show that menu with the most recent fixes included is really
>>> significantly worse on their platform).
>>
>> For all the platforms I've been testing, the teo governor is always the
>> best one.
> 
> Great!  Can you please share any numbers?

There are some at a publication doing an evaluation of the irq 
prediction [1]

>> Using the menu governor has also an impact on the user experience as it
>> lags on mobile.
> 
> Well, I'm not quite sure what you mean here?

For example, the user feels the lag when touching the screen on a mobile 
or scrolling a document. Changing from menu to teo solves this issue.


>> After studying the history of the menu governor few years ago, it
>> appeared the menu governor was introduced before the SMP was widely
>> used. The strength of the menu governor was the ability to find
>> repeating intervals but with he multiplication of the cores, the IPIs
>> were introduced which increased the entropy of the busy-idle cycles
>> duration, thus making the duration much more random and altering the
>> menu governor prediction accuracy.
> 
> While this arguably is the case, menu has also been changed quite a
> bit since its introduction.
> 
> What I'm looking for really is a set of numbers showing the difference
> and clearly pointing out that teo should be preferred.

Ok, let me check if I can find a platform doing energy measurement.

I guess x86 is not a good target as the firmware overcomes the kernel 
decisions right ?


   -- D.


[1] 
https://hal.science/hal-04095844v1/file/O_S_level_interrupt_prediction_for_performance_and_energy_management_on_Android.pdf

-- 
<http://www.linaro.org/> Linaro.org │ Open source software for ARM SoCs

Follow Linaro:  <http://www.facebook.com/pages/Linaro> Facebook |
<http://twitter.com/#!/linaroorg> Twitter |
<http://www.linaro.org/linaro-blog/> Blog