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

Peter Zijlstra
2024-09-11T08:45:40Z

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.