On 5 June 2013 08:54, Xiaoguang Chen chenxg.marvell@gmail.com wrote:
Hi, Guys
Hi Xiaoguang,
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.
Not really.. There are situations when this will not hold true.. If you hot-unplug cpu0, then next cpu in line, i.e. cpu 1, will become policy->cpu :)
in userspace governor, when governor stop is called, it will set per_cpu(cpu_is_managed, cpu) = 0
To make it clear, cpu_is_managed isn't telling which cpu is managing 'cpu' but if governor is enabled for cpu 'cpu' or not.
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:
- 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?
Hmm.. the problem is bigger than what you observed.. I am starting to cleanup userspace governor now and will cc you for my patches. Please test them and give your Tested-by :)