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

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Message-ID: <52ca4cea-8f65-434e-af17-e4bf664d9488@arm.com>
Date: Wed, 11 Sep 2024 09:35:16 +0100
From: Luis Machado <luis.machado@....com>
To: Peter Zijlstra <peterz@...radead.org>
Cc: Dietmar Eggemann <dietmar.eggemann@....com>,
 Vincent Guittot <vincent.guittot@...aro.org>,
 Hongyan Xia <hongyan.xia2@....com>, mingo@...hat.com, juri.lelli@...hat.com,
 rostedt@...dmis.org, bsegall@...gle.com, mgorman@...e.de,
 vschneid@...hat.com, linux-kernel@...r.kernel.org, kprateek.nayak@....com,
 wuyun.abel@...edance.com, youssefesmat@...omium.org, tglx@...utronix.de,
 efault@....de
Subject: Re: [PATCH 10/24] sched/uclamg: Handle delayed dequeue

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.