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Sender: Ingo Molnar <mingo.kernel.org@gmail.com>
Date:   Thu, 5 Oct 2023 13:26:50 +0200
From:   Ingo Molnar <mingo@kernel.org>
To:     Xuewen Yan <xuewen.yan@unisoc.com>
Cc:     rafael@kernel.org, viresh.kumar@linaro.org, mingo@redhat.com,
        peterz@infradead.org, vincent.guittot@linaro.org,
        dietmar.eggemann@arm.com, rostedt@goodmis.org, bsegall@google.com,
        mgorman@suse.de, bristot@redhat.com, vschneid@redhat.com,
        guohua.yan@unisoc.com, qyousef@layalina.io,
        linux-pm@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH] cpufreq: schedutil: next_freq need update when
 cpufreq_limits changed
Message-ID: <ZR6delkbZxl31zuY@gmail.com>
References: <20230719130527.8074-1-xuewen.yan@unisoc.com>
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In-Reply-To: <20230719130527.8074-1-xuewen.yan@unisoc.com>
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* Xuewen Yan <xuewen.yan@unisoc.com> wrote:

> When cpufreq's policy is single, there is a scenario that will
> cause sg_policy's next_freq to be unable to update.
> 
> When the cpu's util is always max, the cpufreq will be max,
> and then if we change the policy's scaling_max_freq to be a
> lower freq, indeed, the sg_policy's next_freq need change to
> be the lower freq, however, because the cpu_is_busy, the next_freq
> would keep the max_freq.
> 
> For example:
> The cpu7 is single cpu:
> 
> unisoc:/sys/devices/system/cpu/cpufreq/policy7 # while true;do done&
> [1] 4737
> unisoc:/sys/devices/system/cpu/cpufreq/policy7 # taskset -p 80 4737
> pid 4737's current affinity mask: ff
> pid 4737's new affinity mask: 80
> unisoc:/sys/devices/system/cpu/cpufreq/policy7 # cat scaling_max_freq
> 2301000
> unisoc:/sys/devices/system/cpu/cpufreq/policy7 # cat scaling_cur_freq
> 2301000
> unisoc:/sys/devices/system/cpu/cpufreq/policy7 # echo 2171000 > scaling_max_freq
> unisoc:/sys/devices/system/cpu/cpufreq/policy7 # cat scaling_max_freq
> 2171000
> 
> At this time, the sg_policy's next_freq would keep 2301000.
> 
> To prevent the case happen, add the judgment of the need_freq_update flag.
> 
> Signed-off-by: Xuewen Yan <xuewen.yan@unisoc.com>
> Co-developed-by: Guohua Yan <guohua.yan@unisoc.com>
> Signed-off-by: Guohua Yan <guohua.yan@unisoc.com>
> ---
>  kernel/sched/cpufreq_schedutil.c | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
> 
> diff --git a/kernel/sched/cpufreq_schedutil.c b/kernel/sched/cpufreq_schedutil.c
> index 4492608b7d7f..458d359f5991 100644
> --- a/kernel/sched/cpufreq_schedutil.c
> +++ b/kernel/sched/cpufreq_schedutil.c
> @@ -350,7 +350,8 @@ static void sugov_update_single_freq(struct update_util_data *hook, u64 time,
>  	 * Except when the rq is capped by uclamp_max.
>  	 */
>  	if (!uclamp_rq_is_capped(cpu_rq(sg_cpu->cpu)) &&
> -	    sugov_cpu_is_busy(sg_cpu) && next_f < sg_policy->next_freq) {
> +	    sugov_cpu_is_busy(sg_cpu) && next_f < sg_policy->next_freq &&
> +	    !sg_policy->need_freq_update) {
>  		next_f = sg_policy->next_freq;
>  
>  		/* Restore cached freq as next_freq has changed */

Just wondering about the status of this fix - is it pending in
some tree, or should we apply it to the scheduler tree?

Thanks,

	Ingo