On Wed, May 9, 2012 at 2:31 PM, Rafael J. Wysocki <rjw@xxxxxxx> wrote:
> On Tuesday, May 08, 2012, Colin Cross wrote:
>> Adds cpuidle_coupled_parallel_barrier, which can be used by coupled
>> cpuidle state enter functions to handle resynchronization after
>> determining if any cpu needs to abort. The normal use case will
>> be:
>>
>> static bool abort_flag;
>> static atomic_t abort_barrier;
>>
>> int arch_cpuidle_enter(struct cpuidle_device *dev, ...)
>> {
>> if (arch_turn_off_irq_controller()) {
>> /* returns an error if an irq is pending and would be lost
>> if idle continued and turned off power */
>> abort_flag = true;
>> }
>>
>> cpuidle_coupled_parallel_barrier(dev, &abort_barrier);
>>
>> if (abort_flag) {
>> /* One of the cpus didn't turn off it's irq controller */
>> arch_turn_on_irq_controller();
>> return -EINTR;
>> }
>>
>> /* continue with idle */
>> ...
>> }
>>
>> This will cause all cpus to abort idle together if one of them needs
>> to abort.
>>
>> Reviewed-by: Santosh Shilimkar <santosh.shilimkar@xxxxxx>
>> Tested-by: Santosh Shilimkar <santosh.shilimkar@xxxxxx>
>> Reviewed-by: Kevin Hilman <khilman@xxxxxx>
>> Tested-by: Kevin Hilman <khilman@xxxxxx>
>> Signed-off-by: Colin Cross <ccross@xxxxxxxxxxx>
>> ---
>> drivers/cpuidle/coupled.c | 37 +++++++++++++++++++++++++++++++++++++
>> include/linux/cpuidle.h | 4 ++++
>> 2 files changed, 41 insertions(+), 0 deletions(-)
>>
>> diff --git a/drivers/cpuidle/coupled.c b/drivers/cpuidle/coupled.c
>> index 93101fb..3e65de1 100644
>> --- a/drivers/cpuidle/coupled.c
>> +++ b/drivers/cpuidle/coupled.c
>> @@ -130,6 +130,43 @@ struct cpuidle_coupled {
>> static cpumask_t cpuidle_coupled_poked_mask;
>>
>> /**
>> + * cpuidle_coupled_parallel_barrier - synchronize all online coupled cpus
>> + * @dev: cpuidle_device of the calling cpu
>> + * @a: atomic variable to hold the barrier
>> + *
>> + * No caller to this function will return from this function until all online
>> + * cpus in the same coupled group have called this function. Once any caller
>> + * has returned from this function, the barrier is immediately available for
>> + * reuse.
>> + *
>> + * The atomic variable a must be initialized to 0 before any cpu calls
>> + * this function, will be reset to 0 before any cpu returns from this function.
>> + *
>> + * Must only be called from within a coupled idle state handler
>> + * (state.enter when state.flags has CPUIDLE_FLAG_COUPLED set).
>> + *
>> + * Provides full smp barrier semantics before and after calling.
>> + */
>> +void cpuidle_coupled_parallel_barrier(struct cpuidle_device *dev, atomic_t *a)
>> +{
>> + int n = dev->coupled->online_count;
>> +
>> + smp_mb__before_atomic_inc();
>> + atomic_inc(a);
>> +
>> + while (atomic_read(a) < n)
>> + cpu_relax();
>> +
>> + if (atomic_inc_return(a) == n * 2) {
>> + atomic_set(a, 0);
>> + return;
>> + }
>> +
>> + while (atomic_read(a) > n)
>> + cpu_relax();
>> +}
>
> Well, this looks like "wait until all CPUs execute this code". Don't we have
> anything like this already somewhere?
>
>> +
>> +/**
>> * cpuidle_state_is_coupled - check if a state is part of a coupled set
>> * @dev: struct cpuidle_device for the current cpu
>> * @drv: struct cpuidle_driver for the platform
>> diff --git a/include/linux/cpuidle.h b/include/linux/cpuidle.h
>> index 6038448..5ab7183 100644
>> --- a/include/linux/cpuidle.h
>> +++ b/include/linux/cpuidle.h
>> @@ -183,6 +183,10 @@ static inline int cpuidle_wrap_enter(struct cpuidle_device *dev,
>>
>> #endif
>>
>> +#ifdef CONFIG_ARCH_NEEDS_CPU_IDLE_COUPLED
>> +void cpuidle_coupled_parallel_barrier(struct cpuidle_device *dev, atomic_t *a);
>> +#endif
>
> Why exactly is the extra Kconfig option necessary?
It prevents compiling in coupled.o (2k text section) on the majority
of kernels that will never use it.
_______________________________________________
linux-pm mailing list
linux-pm@xxxxxxxxxxxxxxxxxxxxxxxxxx
https://lists.linuxfoundation.org/mailman/listinfo/linux-pm
