linux-kernel - Re: [PATCH] cpufreq: schedutil: Update cached "current frequency" when limits change

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Date:   Thu, 13 Jul 2017 18:52:18 -0700
From:   Saravana Kannan <skannan@...eaurora.org>
To:     Viresh Kumar <viresh.kumar@...aro.org>
CC:     "Rafael J. Wysocki" <rjw@...ysocki.net>, linux-pm@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] cpufreq: schedutil: Update cached "current frequency"
 when limits change

On 07/11/2017 10:24 PM, Viresh Kumar wrote:
> On 11-07-17, 19:24, Saravana Kannan wrote:
>> Currently, the governor calculates the next frequency, set the current CPU
>> frequency (policy->cur). It also assumes the current CPU frequency doesn't
>> change if the next frequency isn't calculated again and hence caches the
>> "current frequency".
>>
>> However, this isn't true when CPU min/max frequency limits are changed. So,
>> there's room for the CPU frequency to get stuck at the wrong level if the
>> calculated next frequency doesn't change across multiple limits updates.
>>
>> Fix this by updating the cached "current frequency" when limits changes the
>> current CPU frequency.
>>
>> Signed-off-by: Saravana Kannan <skannan@...eaurora.org>
>> ---
>>   kernel/sched/cpufreq_schedutil.c | 6 ++++++
>>   1 file changed, 6 insertions(+)
>>
>> diff --git a/kernel/sched/cpufreq_schedutil.c b/kernel/sched/cpufreq_schedutil.c
>> index 076a2e3..fe0b2fb 100644
>> --- a/kernel/sched/cpufreq_schedutil.c
>> +++ b/kernel/sched/cpufreq_schedutil.c
>> @@ -226,6 +226,7 @@ static void sugov_update_single(struct update_util_data *hook, u64 time,
>>
>>   	busy = sugov_cpu_is_busy(sg_cpu);
>>
>> +	raw_spin_lock(&sg_policy->update_lock);
>>   	if (flags & SCHED_CPUFREQ_RT_DL) {
>>   		next_f = policy->cpuinfo.max_freq;
>>   	} else {
>> @@ -240,6 +241,7 @@ static void sugov_update_single(struct update_util_data *hook, u64 time,
>>   			next_f = sg_policy->next_freq;
>>   	}
>>   	sugov_update_commit(sg_policy, time, next_f);
>> +	raw_spin_unlock(&sg_policy->update_lock);
>
> We wouldn't allow locking here until the time we can :)
>

Actually, can you clarify why you can't allow locking here?

-Saravana

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