Re: [PATCH 10/24] sched/uclamg: Handle delayed dequeue

[Luis Machado]

On 9/11/24 09:45, Peter Zijlstra wrote:
> On Wed, Sep 11, 2024 at 09:35:16AM +0100, Luis Machado wrote:
>> On 9/10/24 15:05, Peter Zijlstra wrote:
>>> On Tue, Sep 10, 2024 at 12:04:11PM +0100, Luis Machado wrote:
>>>> I gave the above patch a try on our Android workload running on the Pixel 6 with a 6.8-based kernel.
>>>>
>>>> First I'd like to confirm that Dietmar's fix that was pushed to tip:sched/core (Fix util_est
>>>> accounting for DELAY_DEQUEUE) helps bring the frequencies and power use down to more sensible levels.
>>>>
>>>> As for the above changes, unfortunately I'm seeing high frequencies and high power usage again. The
>>>> pattern looks similar to what we observed with the uclamp inc/dec imbalance.
>>>
>>> :-(
>>>
>>>> I haven't investigated this in depth yet, but I'll go stare at some traces and the code, and hopefully
>>>> something will ring bells.
>>>
>>> So first thing to do is trace h_nr_delayed I suppose, in my own
>>> (limited) testing that was mostly [0,1] correctly correlating to there
>>> being a delayed task on the runqueue.
>>>
>>> I'm assuming that removing the usage sites restores function?
>>
>> It does restore function if we remove the usage.
>>
>> From an initial look:
>>
>> cat /sys/kernel/debug/sched/debug | grep -i delay                                                                                                                                                                                                                             
>>   .h_nr_delayed                  : -4
>>   .h_nr_delayed                  : -6
>>   .h_nr_delayed                  : -1
>>   .h_nr_delayed                  : -6
>>   .h_nr_delayed                  : -1
>>   .h_nr_delayed                  : -1
>>   .h_nr_delayed                  : -5
>>   .h_nr_delayed                  : -6
>>
>> So probably an unexpected decrement or lack of an increment somewhere.
> 
> Yeah, that's buggered. Ok, I'll go rebase sched/core and take this patch
> out. I'll see if I can reproduce that.

Before reverting it, let me run a few more checks first. Dietmar tells me
he sees sane values for h_nr_delayed on a juno system.

I just want to make sure I'm not hitting some oddness with the 6.8 kernel
on the pixel 6.