6.1-stable review patch. If anyone has any objections, please let me know. ------------------ From: Xuewen Yan <xuewen.yan@xxxxxxxxxx> [ Upstream commit 9e0bc36ab07c550d791bf17feeb479f1dfc42d89 ] 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 a 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 stay at 2301000, which is wrong. To fix this, add a check for the ->need_freq_update flag. [ mingo: Clarified the changelog. ] Co-developed-by: Guohua Yan <guohua.yan@xxxxxxxxxx> Signed-off-by: Xuewen Yan <xuewen.yan@xxxxxxxxxx> Signed-off-by: Guohua Yan <guohua.yan@xxxxxxxxxx> Signed-off-by: Ingo Molnar <mingo@xxxxxxxxxx> Acked-by: "Rafael J. Wysocki" <rafael@xxxxxxxxxx> Link: https://lore.kernel.org/r/20230719130527.8074-1-xuewen.yan@xxxxxxxxxx Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx> --- 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 1207c78f85c11..853a07618a3cf 100644 --- a/kernel/sched/cpufreq_schedutil.c +++ b/kernel/sched/cpufreq_schedutil.c @@ -345,7 +345,8 @@ 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 */ -- 2.40.1
