From 20ff51a36b2cd25ee7eb3216b6d02b68935435ba Mon Sep 17 00:00:00 2001 From: Colin Cross Date: Mon, 7 May 2012 17:57:42 -0700 Subject: [PATCH] cpuidle: coupled: add parallel barrier function 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 Tested-by: Santosh Shilimkar Reviewed-by: Kevin Hilman Tested-by: Kevin Hilman Signed-off-by: Colin Cross Signed-off-by: Len Brown --- drivers/cpuidle/coupled.c | 37 +++++++++++++++++++++++++++++++++++++ include/linux/cpuidle.h | 4 ++++ 2 files changed, 41 insertions(+) diff --git a/drivers/cpuidle/coupled.c b/drivers/cpuidle/coupled.c index aab6bba8daec..2c9bf2692232 100644 --- a/drivers/cpuidle/coupled.c +++ b/drivers/cpuidle/coupled.c @@ -129,6 +129,43 @@ static DEFINE_PER_CPU(struct call_single_data, cpuidle_coupled_poke_cb); */ 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 diff --git a/include/linux/cpuidle.h b/include/linux/cpuidle.h index 603844835bc7..5ab7183313ce 100644 --- a/include/linux/cpuidle.h +++ b/include/linux/cpuidle.h @@ -183,6 +183,10 @@ static inline int cpuidle_play_dead(void) {return -ENODEV; } #endif +#ifdef CONFIG_ARCH_NEEDS_CPU_IDLE_COUPLED +void cpuidle_coupled_parallel_barrier(struct cpuidle_device *dev, atomic_t *a); +#endif + /****************************** * CPUIDLE GOVERNOR INTERFACE * ******************************/ -- 2.34.1