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Message-ID: <6b909593-ffc2-4fbb-b49a-143ef1fb42d7@arm.com>
Date: Tue, 11 Jun 2024 10:08:28 +0100
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Subject: Re: [PATCH] sched/fair: Prevent cpu_busy_time from exceeding
 actual_cpu_capacity
To: Xuewen Yan <xuewen.yan@unisoc.com>, vincent.guittot@linaro.org,
 mingo@redhat.com, peterz@infradead.org, juri.lelli@redhat.com,
 dietmar.eggemann@arm.com
Cc: rostedt@goodmis.org, bsegall@google.com, mgorman@suse.de,
 bristot@redhat.com, vschneid@redhat.com, vincent.donnefort@arm.com,
 qyousef@layalina.io, ke.wang@unisoc.com, xuewen.yan94@gmail.com,
 linux-kernel@vger.kernel.org
References: <20240606070645.3295-1-xuewen.yan@unisoc.com>
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From: Christian Loehle <christian.loehle@arm.com>
In-Reply-To: <20240606070645.3295-1-xuewen.yan@unisoc.com>
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On 6/6/24 08:06, Xuewen Yan wrote:
> Because the effective_cpu_util() would return a util which
> maybe bigger than the actual_cpu_capacity, this could cause
> the pd_busy_time calculation errors.
> So clamp the cpu_busy_time with the eenv->cpu_cap, which is
> the actual_cpu_capacity.
> 
> Fixes: 3e8c6c9aac42 ("sched/fair: Remove task_util from effective utilization in feec()")
> Signed-off-by: Xuewen Yan <xuewen.yan@unisoc.com>
> ---
>  kernel/sched/fair.c | 4 +++-
>  1 file changed, 3 insertions(+), 1 deletion(-)
> 
> diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
> index 8a5b1ae0aa55..8939d725023a 100644
> --- a/kernel/sched/fair.c
> +++ b/kernel/sched/fair.c
> @@ -7870,7 +7870,9 @@ static inline void eenv_pd_busy_time(struct energy_env *eenv,
>  	for_each_cpu(cpu, pd_cpus) {
>  		unsigned long util = cpu_util(cpu, p, -1, 0);
>  
> -		busy_time += effective_cpu_util(cpu, util, NULL, NULL);
> +		util = effective_cpu_util(cpu, util, NULL, NULL);
> +		util = min(eenv->cpu_cap, util);
> +		busy_time += util;
>  	}
>  
>  	eenv->pd_busy_time = min(eenv->pd_cap, busy_time);

I can reproduce the issue and the fix, so
Tested-by: Christian Loehle <christian.loehle@arm.com>
(@Qais, this is on a non-overutilized system).
I'm unsure about the other callers of effective_cpu_util(), or rather sched_cpu_util()
in particular which includes thermal and powercap, they should be off too.
Anyway I'll try to reproduce for them too.

Kind Regards,
Christian