Re: [PATCHv2 3/5] cpuidle: add support for states that affect multiple cpus

[Colin Cross <ccross@android.com>]

On Thu, Mar 15, 2012 at 5:04 PM, Kevin Hilman <khilman@ti.com> wrote:
> Colin Cross <ccross@android.com> writes:
>
>> +/**
>> + * cpuidle_coupled_cpu_set_alive - adjust alive_count during hotplug transitions
>> + * @cpu: target cpu number
>> + * @alive: whether the target cpu is going up or down
>> + *
>> + * Run on the cpu that is bringing up the target cpu, before the target cpu
>> + * has been booted, or after the target cpu is completely dead.
>> + */
>> +static void cpuidle_coupled_cpu_set_alive(int cpu, bool alive)
>> +{
>> +     struct cpuidle_device *dev;
>> +     struct cpuidle_coupled *coupled;
>> +
>> +     mutex_lock(&cpuidle_lock);
>> +
>> +     dev = per_cpu(cpuidle_devices, cpu);
>> +     if (!dev->coupled)
>> +             goto out;
>> +
>> +     coupled = dev->coupled;
>> +
>> +     /*
>> +      * waiting_count must be at least 1 less than alive_count, because
>> +      * this cpu is not waiting.  Spin until all cpus have noticed this cpu
>> +      * is not idle and exited the ready loop before changing alive_count.
>> +      */
>> +     while (atomic_read(&coupled->ready_count))
>> +             cpu_relax();
>> +
>> +     smp_mb__before_atomic_inc();
>> +     atomic_inc(&coupled->alive_count);
>
> This doesn't look quite right.  alive_count is incrmented whether the
> CPU is going up or down?
>
> Maybe I misunderstood something, but I don't see anywhere where
> alive_count is decrmemented after a CPU is removed.

Oops, dropped the atomic_dec when I merged from two separate functions
for up and down to a single function that takes a bool.

>> +     smp_mb__after_atomic_inc();
>> +
>> +     if (alive)
>> +             coupled->requested_state[dev->cpu] = CPUIDLE_COUPLED_NOT_IDLE;
>> +     else
>> +             coupled->requested_state[dev->cpu] = CPUIDLE_COUPLED_DEAD;
>> +
>> +out:
>> +     mutex_unlock(&cpuidle_lock);
>> +}
>> +