linux-kernel - Re: [GIT PULL] Scheduler changes for v6.8

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Date: Thu, 11 Jan 2024 09:45:15 -0800
From: Linus Torvalds <torvalds@...ux-foundation.org>
To: Vincent Guittot <vincent.guittot@...aro.org>
Cc: Ingo Molnar <mingo@...nel.org>, linux-kernel@...r.kernel.org, 
	Peter Zijlstra <peterz@...radead.org>, Thomas Gleixner <tglx@...utronix.de>, 
	Juri Lelli <juri.lelli@...hat.com>, Dietmar Eggemann <dietmar.eggemann@....com>, 
	Steven Rostedt <rostedt@...dmis.org>, Ben Segall <bsegall@...gle.com>, Mel Gorman <mgorman@...e.de>, 
	Daniel Bristot de Oliveira <bristot@...hat.com>, Valentin Schneider <vschneid@...hat.com>
Subject: Re: [GIT PULL] Scheduler changes for v6.8

On Thu, 11 Jan 2024 at 00:11, Vincent Guittot
<vincent.guittot@...aro.org> wrote:
>
> Could you confirm that cpufreq governor is schedutil and the driver is
> amd-pstate on your system ?

schedutil yes, amd-pstate no. I actually just use acpi_cpufreq

>
> Also I'm interested by the output of the amd_pstate to confirm that it uses the
> adjust_perf callback
>
> I suppose that you don't use uclamp feature and amd doesn't use EAS so that let
> the change of the min parameter of adjust_perf which was probably always 0
> unless you use deadline scheduler and which now takes into account irq pressure.
>
> Could you try the patch below which restores the previous min value ?
>
> ---
>  kernel/sched/cpufreq_schedutil.c | 5 +++--
>  1 file changed, 3 insertions(+), 2 deletions(-)
>
> diff --git a/kernel/sched/cpufreq_schedutil.c b/kernel/sched/cpufreq_schedutil.c
> index 95c3c097083e..3fe8ac6ce9cc 100644
> --- a/kernel/sched/cpufreq_schedutil.c
> +++ b/kernel/sched/cpufreq_schedutil.c
> @@ -194,10 +194,11 @@ unsigned long sugov_effective_cpu_perf(int cpu, unsigned long actual,
>  static void sugov_get_util(struct sugov_cpu *sg_cpu, unsigned long boost)
>  {
>         unsigned long min, max, util = cpu_util_cfs_boost(sg_cpu->cpu);
> +       struct rq *rq = cpu_rq(sg_cpu->cpu);
>
>         util = effective_cpu_util(sg_cpu->cpu, util, &min, &max);
>         util = max(util, boost);
> -       sg_cpu->bw_min = min;
> +       sg_cpu->bw_min = cpu_bw_dl(rq);
>         sg_cpu->util = sugov_effective_cpu_perf(sg_cpu->cpu, util, min, max);
>  }
>
> @@ -442,7 +443,7 @@ static void sugov_update_single_perf(struct update_util_data *hook, u64 time,
>             sugov_cpu_is_busy(sg_cpu) && sg_cpu->util < prev_util)
>                 sg_cpu->util = prev_util;
>
> -       cpufreq_driver_adjust_perf(sg_cpu->cpu, sg_cpu->bw_min,
> +       cpufreq_driver_adjust_perf(sg_cpu->cpu, map_util_perf(sg_cpu->bw_min),
>                                    sg_cpu->util, max_cap);
>
>         sg_cpu->sg_policy->last_freq_update_time = time;
> --
> 2.34.1
>
>
> >
> > I'll keep that revert in my private test-tree for now (so that I have
> > a working machine again), but I'll move it to my main branch soon
> > unless somebody has a quick fix for this problem.
> >
> >                 Linus