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

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <20240911084528.GJ4723@noisy.programming.kicks-ass.net>
Date: Wed, 11 Sep 2024 10:45:28 +0200
From: Peter Zijlstra <peterz@...radead.org>
To: Luis Machado <luis.machado@....com>
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 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.