Hi Rafael and other cpufreq masters,

I am really not sure if this patch is a HACK or a valid solution :) Please have a look.

Setup: ----- - ARM big LITTLE Platform with 5 cpus. cpus 2, 3 & 4 share clock and hence are part of policy->cpus. cpus 0 & 1 share clock but they aren't discussed here. - Interactive governor: I know its not mainlined and will never be. Problem should be same with all the governors we have. So, problem is not really governor dependent. I have added few prints at start/stop cases of governor, to see what policy->cpus is set to.

Problem Statement: ----------------- There are many issues :(

1) I couldn't understand what we really want the value of policy->cpus be? Only the online cpus sharing clock? or all the possible cpus sharing clock?

When we offline a cpu, we remove it from cpus field: cpumask_clear_cpu(cpu, data->cpus);

Which shows that it is mask of online cpus only. But there are many places checking if a cpu is online or not (cpu in policy->cpus) in cpufreq.c. Which shows something else.

2) Kernel crashes when hot-unplugging cpus

When we do: for i in 2 3 4; do echo 0 > /sys/devices/system/cpu/cpu$i/online; done We get:

cpufreq_governor_interactive: CPUFREQ_GOV_STOP cpu 2 policy->cpus 2-4 cpufreq_vexpress: CPUFreq for CPU 3 initialized cpufreq_governor_interactive: CPUFREQ_GOV_START cpu 3 policy->cpus 2-4 CPU2: shutdown cpufreq_governor_interactive: CPUFREQ_GOV_STOP cpu 3 policy->cpus 3-4 cpufreq_vexpress: CPUFreq for CPU 4 initialized cpufreq_governor_interactive: CPUFREQ_GOV_START cpu 4 policy->cpus 2-4

And then crash from interactive governor.

Note the following lines: ------------------------ cpufreq_governor_interactive: CPUFREQ_GOV_STOP cpu 2 policy->cpus 2-4 cpufreq_governor_interactive: CPUFREQ_GOV_START cpu 3 policy->cpus 2-4 cpufreq_governor_interactive: CPUFREQ_GOV_STOP cpu 3 policy->cpus 3-4 cpufreq_governor_interactive: CPUFREQ_GOV_START cpu 4 policy->cpus 2-4

So the governor is always started for CPUs 2 through 4 despite the fact that CPU 2 is removed. This makes the governor unstable due to wrong info passed.

FIX: keep only online cpus in policy->cpus ---

3) With above issue solved, i tried to run the same stuff again and look what i got:

cpufreq_governor_interactive: CPUFREQ_GOV_STOP cpu 2 policy->cpus 2-4 cpufreq_vexpress: CPUFreq for CPU 3 initialized cpufreq_governor_interactive: CPUFREQ_GOV_START cpu 3 policy->cpus 2-4 CPU2: shutdown

a) Because cpu 2 is still not completely hot unplugged and is still present in cpu_online_mask. b) If we try to remove cpu 3, governor wouldn't be notified of it, because cpu 3 wasn't policy->cpu.

FIX: Stop/Start governor on every non policy->cpu removal ---

4) Hot unplug is fine now, but not hotplug :( for i in 2 3 4; do echo 1 > /sys/devices/system/cpu/cpu$i/online; done

CPU2: Booted secondary processor cpufreq_vexpress: CPUFreq for CPU 2 initialized cpufreq_governor_interactive: CPUFREQ_GOV_START cpu 2 policy->cpus 2 CPU3: Booted secondary processor cpufreq_vexpress: CPUFreq for CPU 3 initialized CPU4: Booted secondary processor cpufreq_vexpress: CPUFreq for CPU 4 initialized

Hmmm, Governor is not informed about 3 and 4. :(

FIX: Stop/Start governor on every managed_policy cpu, i.e. cpu for which --- policy struct exists

Please share your comments, i know there would be many :)

Signed-off-by: Viresh Kumar viresh.kumar@linaro.org --- drivers/cpufreq/cpufreq.c | 17 +++++++++++++++++ 1 file changed, 17 insertions(+)

diff --git a/drivers/cpufreq/cpufreq.c b/drivers/cpufreq/cpufreq.c index 0c3e29a..69bd739 100644 --- a/drivers/cpufreq/cpufreq.c +++ b/drivers/cpufreq/cpufreq.c @@ -749,11 +749,16 @@ static int cpufreq_add_dev_policy(unsigned int cpu, return -EBUSY; }

+ __cpufreq_governor(managed_policy, CPUFREQ_GOV_STOP); + spin_lock_irqsave(&cpufreq_driver_lock, flags); cpumask_copy(managed_policy->cpus, policy->cpus); per_cpu(cpufreq_cpu_data, cpu) = managed_policy; spin_unlock_irqrestore(&cpufreq_driver_lock, flags);

+ __cpufreq_governor(managed_policy, CPUFREQ_GOV_START); + __cpufreq_governor(managed_policy, CPUFREQ_GOV_LIMITS); + pr_debug("CPU already managed, adding link\n"); ret = sysfs_create_link(&dev->kobj, &managed_policy->kobj, @@ -968,6 +973,13 @@ static int cpufreq_add_dev(struct device *dev, struct subsys_interface *sif) pr_debug("initialization failed\n"); goto err_unlock_policy; } + + /* + * affected cpus must always be the one, which are online. We aren't + * managing offline cpus here. + */ + cpumask_and(policy->cpus, policy->cpus, cpu_online_mask); + policy->user_policy.min = policy->min; policy->user_policy.max = policy->max;

@@ -1057,8 +1069,13 @@ static int __cpufreq_remove_dev(struct device *dev, struct subsys_interface *sif */ if (unlikely(cpu != data->cpu)) { pr_debug("removing link\n"); + __cpufreq_governor(data, CPUFREQ_GOV_STOP); cpumask_clear_cpu(cpu, data->cpus); spin_unlock_irqrestore(&cpufreq_driver_lock, flags); + + __cpufreq_governor(data, CPUFREQ_GOV_START); + __cpufreq_governor(data, CPUFREQ_GOV_LIMITS); + kobj = &dev->kobj; cpufreq_cpu_put(data); unlock_policy_rwsem_write(cpu);