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

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Date: Sun, 14 Jan 2024 14:02:46 +0100
From: Dietmar Eggemann <dietmar.eggemann@....com>
To: Wyes Karny <wkarny@...il.com>,
 Vincent Guittot <vincent.guittot@...aro.org>
Cc: Linus Torvalds <torvalds@...ux-foundation.org>,
 Qais Yousef <qyousef@...alina.io>, 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>,
 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 14/01/2024 13:37, Wyes Karny wrote:
> On Sun, Jan 14, 2024 at 12:18:06PM +0100, Vincent Guittot wrote:
>> Hi Wyes,
>>
>> Le dimanche 14 janv. 2024 ï¿½ 14:42:40 (+0530), Wyes Karny a ï¿½crit :
>>> On Wed, Jan 10, 2024 at 02:57:14PM -0800, Linus Torvalds wrote:
>>>> On Wed, 10 Jan 2024 at 14:41, Linus Torvalds
>>>> <torvalds@...ux-foundation.org> wrote:

[...]

> Yeah, correct something was wrong in the bpftrace readings, max_cap is
> not zero in traces.
> 
>              git-5511    [001] d.h1.   427.159763: get_next_freq.constprop.0: [DEBUG] : freq 1400000, util 1024, max 1024
>              git-5511    [001] d.h1.   427.163733: sugov_get_util: [DEBUG] : util 1024, sg_cpu->util 1024
>              git-5511    [001] d.h1.   427.163735: get_next_freq.constprop.0: [DEBUG] : freq 1400000, util 1024, max 1024
>              git-5511    [001] d.h1.   427.167706: sugov_get_util: [DEBUG] : util 1024, sg_cpu->util 1024
>              git-5511    [001] d.h1.   427.167708: get_next_freq.constprop.0: [DEBUG] : freq 1400000, util 1024, max 1024
>              git-5511    [001] d.h1.   427.171678: sugov_get_util: [DEBUG] : util 1024, sg_cpu->util 1024
>              git-5511    [001] d.h1.   427.171679: get_next_freq.constprop.0: [DEBUG] : freq 1400000, util 1024, max 1024
>              git-5511    [001] d.h1.   427.175653: sugov_get_util: [DEBUG] : util 1024, sg_cpu->util 1024
>              git-5511    [001] d.h1.   427.175655: get_next_freq.constprop.0: [DEBUG] : freq 1400000, util 1024, max 1024
>              git-5511    [001] d.s1.   427.175665: sugov_get_util: [DEBUG] : util 1024, sg_cpu->util 1024
>              git-5511    [001] d.s1.   427.175665: get_next_freq.constprop.0: [DEBUG] : freq 1400000, util 1024, max 1024
> 
> Debug patch applied:
> 
> diff --git a/kernel/sched/cpufreq_schedutil.c b/kernel/sched/cpufreq_schedutil.c
> index 95c3c097083e..5c9b3e1de7a0 100644
> --- a/kernel/sched/cpufreq_schedutil.c
> +++ b/kernel/sched/cpufreq_schedutil.c
> @@ -166,6 +166,7 @@ static unsigned int get_next_freq(struct sugov_policy *sg_policy,
> 
>         freq = get_capacity_ref_freq(policy);
>         freq = map_util_freq(util, freq, max);
> +       trace_printk("[DEBUG] : freq %llu, util %llu, max %llu\n", freq, util, max);
> 
>         if (freq == sg_policy->cached_raw_freq && !sg_policy->need_freq_update)
>                 return sg_policy->next_freq;
> @@ -199,6 +200,7 @@ static void sugov_get_util(struct sugov_cpu *sg_cpu, unsigned long boost)
>         util = max(util, boost);
>         sg_cpu->bw_min = min;
>         sg_cpu->util = sugov_effective_cpu_perf(sg_cpu->cpu, util, min, max);
> +       trace_printk("[DEBUG] : util %llu, sg_cpu->util %llu\n", util, sg_cpu->util);
>  }
> 
>  /**
> 
> 
> So, I guess map_util_freq going wrong somewhere.

sugov_update_single_freq() -> get_next_freq() -> get_capacity_ref_freq()

Is arch_scale_freq_invariant() true in both cases, so that
get_capacity_ref_freq() returns 'policy->cpuinfo.max_freq' and not just
'policy->cur'?