Hi, Guys
I met another question for cpufreq governor. When hotplug out one cpu,
cpufreq will remove the cpu device and also call governor stop, if
there are more than 1 cpu and cpu0 is the root for cpufreq, other cpus
are linked to cpu0. then policy->cpu is 0 always.
in userspace governor, when governor stop is called, it will set
per_cpu(cpu_is_managed, cpu) = 0
but the cpu is policy->cpu which is 0 always.
case CPUFREQ_GOV_STOP:
mutex_lock(&userspace_mutex);
cpus_using_userspace_governor--;
if (cpus_using_userspace_governor == 0) {
cpufreq_unregister_notifier(
&userspace_cpufreq_notifier_block,
CPUFREQ_TRANSITION_NOTIFIER);
}
per_cpu(cpu_is_managed, cpu) = 0;
per_cpu(cpu_min_freq, cpu) = 0;
per_cpu(cpu_max_freq, cpu) = 0;
per_cpu(cpu_set_freq, cpu) = 0;
pr_debug("managing cpu %u stopped\n", cpu);
mutex_unlock(&userspace_mutex);
break;
also in userspace governor store_setspeed function cpufreq_set will
retun error if per_cpu(cpu_is_managed, cpu) is 0 which means it will
not change frequency .
static int cpufreq_set(struct cpufreq_policy *policy, unsigned int freq)
{
int ret = -EINVAL;
pr_debug("cpufreq_set for cpu %u, freq %u kHz\n", policy->cpu, freq);
mutex_lock(&userspace_mutex);
if (!per_cpu(cpu_is_managed, policy->cpu))
goto err;
per_cpu(cpu_set_freq, policy->cpu) = freq;
...........
So consider below case:
1) cpu0 tries to hotplug cpu3, it calls userspace governor stop
function, it should stop cpu3's userspace governor, but it actually
set cpu0's per_cpu(cpu_is_managed, cpu) to 0.
2) cpu0 tries to change cpu freuqency through userspace governor, but
it will never succeed since cpufreq_set will return err if cpu0'
percpu variable cpu_is_managed is 0.
3) unless there is another cpu hotplug in operation, in which it calls
governor start and set cpu_is_managed to 1, then the frequency change
will go on and doesn't report error.
The reason here is policy->cpu is always 0 if we use managed policy
for all cpus. but we can't see which cpu's governor want's to
start/stop in userspace goveror. we can only get the information from
struct policy, but this policy doesn't include the exact cpu that
wants to do governor start/stop.
Any suggestions for this issue?
Thanks
Xiaoguang
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