Re: [PATCH v4 6/7] cpufreq: Support for fast frequency switching

Peter Zijlstra
2016-03-16T15:43:14Z

On Wed, Mar 16, 2016 at 03:52:28PM +0100, Rafael J. Wysocki wrote:
> +void cpufreq_enable_fast_switch(struct cpufreq_policy *policy)
> +{
> + mutex_lock(&cpufreq_fast_switch_lock);
> + if (policy->fast_switch_possible && cpufreq_fast_switch_count >= 0) {
> + cpufreq_fast_switch_count++;
> + policy->fast_switch_enabled = true;
> + } else {
> + pr_warn("cpufreq: CPU%u: Fast freqnency switching not enabled\n",
> + policy->cpu);

This happens because there's transition notifiers, right? Would it make
sense to iterate the notifier here and print the notifier function
symbol for each? That way we've got a clue as to where to start looking
when this happens.

> + }
> + mutex_unlock(&cpufreq_fast_switch_lock);
> +}

> @@ -1653,8 +1703,18 @@ int cpufreq_register_notifier(struct not
>
> switch (list) {
> case CPUFREQ_TRANSITION_NOTIFIER:
> + mutex_lock(&cpufreq_fast_switch_lock);
> +
> + if (cpufreq_fast_switch_count > 0) {
> + mutex_unlock(&cpufreq_fast_switch_lock);

So while theoretically (it has a return code)
cpufreq_register_notifier() could fail, it never actually did. Now we
do. Do we want to add a WARN here?

> + return -EPERM;
> + }
> ret = srcu_notifier_chain_register(
> &cpufreq_transition_notifier_list, nb);
> + if (!ret)
> + cpufreq_fast_switch_count--;
> +
> + mutex_unlock(&cpufreq_fast_switch_lock);
> break;
> case CPUFREQ_POLICY_NOTIFIER:
> ret = blocking_notifier_chain_register(