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Message-ID: <20230721221944.dthg3tf25j4qgc2z@airbuntu>
Date: Fri, 21 Jul 2023 23:19:44 +0100
From: Qais Yousef <qyousef@...alina.io>
To: Xuewen Yan <xuewen.yan@...soc.com>
Cc: rafael@...nel.org, viresh.kumar@...aro.org, mingo@...hat.com,
peterz@...radead.org, vincent.guittot@...aro.org,
dietmar.eggemann@....com, rostedt@...dmis.org, bsegall@...gle.com,
mgorman@...e.de, bristot@...hat.com, vschneid@...hat.com,
guohua.yan@...soc.com, linux-pm@...r.kernel.org,
linux-kernel@...r.kernel.org
Subject: Re: [PATCH] cpufreq: schedutil: next_freq need update when
cpufreq_limits changed
On 07/19/23 21:05, Xuewen Yan 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@...soc.com>
> Co-developed-by: Guohua Yan <guohua.yan@...soc.com>
> Signed-off-by: Guohua Yan <guohua.yan@...soc.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) {
What about sugov_update_single_perf()? It seems to have the same problem, no?
LGTM otherwise.
Cheers
--
Qais Yousef
> next_f = sg_policy->next_freq;
>
> /* Restore cached freq as next_freq has changed */
> --
> 2.25.1
>
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