Re: [RFC][PATCH 08/10] sched/fair: Implement delayed dequeue

Hongyan Xia
2024-06-03T15:57:23Z

On 23/05/2024 10:33, Peter Zijlstra wrote:
> On Thu, May 23, 2024 at 10:06:04AM +0100, Luis Machado wrote:
>
>> Booting the kernel with NO_DELAY_DEQUEUE (default to false), things work fine. Then
>> if I switch to DELAY_DEQUEUE at runtime, things start using a lot more power.
>>
>> The interesting bit is if I switch to NO_DELAY_DEQUEUE again at runtime, things don't
>> go back to normal. Rather they stay the same, using a lot more energy.
>
> Ooh, cute.. weird. I'll try and see if we leak state somehow.

Hi. I'm working on uclamp anyway so I just gave this series (and all
fixes mentioned in this thread) a go.

It seems after running with this series for a while, suddenly uclamp_max
no longer works. Running a task with uclamp_max of 110 still sees an rq
uclamp_max of 1024. Also weirdly, the PELT signal of that uclamp_max is
completely broken. It goes up to a very high value and then suddenly
drops to almost 0 from time to time.

I wonder if the reason Luis saw that is because he was the first one to
run delayed dequeue with uclamp. I'm not familiar enough with the series
to know how it could possibly affect uclamp so investigating in this
front may be worth trying. Maybe some leaked uclamp state on the rq?