From mboxrd@z Thu Jan  1 00:00:00 1970
From: ccross@android.com (Colin Cross)
Date: Thu, 15 Mar 2012 17:20:08 -0700
Subject: [PATCHv2 3/5] cpuidle: add support for states that affect
 multiple cpus
In-Reply-To: <87lin18l7o.fsf@ti.com>
References: <1331749794-8056-1-git-send-email-ccross@android.com>
 <1331749794-8056-4-git-send-email-ccross@android.com>
 <87lin18l7o.fsf@ti.com>
Message-ID: <CAMbhsRS3J2vruru8i4r1-cB9aJLYW9y1bP0vv7=L3q1JP77ttg@mail.gmail.com>
To: linux-arm-kernel@lists.infradead.org
List-Id: linux-arm-kernel.lists.infradead.org

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);
>> +}
>> +