linux-kernel - [PATCH] cpufreq: schedutil: next_freq need update when cpufreq

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Date:   Wed, 19 Jul 2023 21:05:27 +0800
From:   Xuewen Yan <xuewen.yan@...soc.com>
To:     <rafael@...nel.org>, <viresh.kumar@...aro.org>, <mingo@...hat.com>,
        <peterz@...radead.org>, <vincent.guittot@...aro.org>
CC:     <dietmar.eggemann@....com>, <rostedt@...dmis.org>,
        <bsegall@...gle.com>, <mgorman@...e.de>, <bristot@...hat.com>,
        <vschneid@...hat.com>, <guohua.yan@...soc.com>,
        <qyousef@...alina.io>, <linux-pm@...r.kernel.org>,
        <linux-kernel@...r.kernel.org>
Subject: [PATCH] cpufreq: schedutil: next_freq need update when cpufreq_limits changed

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) {
 		next_f = sg_policy->next_freq;
 
 		/* Restore cached freq as next_freq has changed */
-- 
2.25.1