[PATCHv4 4/4] cpuidle: coupled: add parallel barrier function
From: Colin Cross <hidden>
Date: 2012-05-08 00:58:00
Also in:
linux-pm, lkml
Subsystem:
cpu idle time management framework, the rest · Maintainers:
"Rafael J. Wysocki", Daniel Lezcano, Linus Torvalds
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 <redacted>
Tested-by: Santosh Shilimkar <redacted>
Reviewed-by: Kevin Hilman <redacted>
Tested-by: Kevin Hilman <redacted>
Signed-off-by: Colin Cross <redacted>
---
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(); +} + +/** * 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 + /****************************** * CPUIDLE GOVERNOR INTERFACE * ******************************/
--
1.7.7.3