[PATCH 18/52] cpuidle: coupled: add parallel barrier function

Len Brown
2012-07-25T03:52:08Z

From: Colin Cross <ccross@android.com>

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@ti.com>
Tested-by: Santosh Shilimkar <santosh.shilimkar@ti.com>
Reviewed-by: Kevin Hilman <khilman@ti.com>
Tested-by: Kevin Hilman <khilman@ti.com>
Signed-off-by: Colin Cross <ccross@android.com>
Signed-off-by: Len Brown <len.brown@intel.com>
---
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 aab6bba..2c9bf26 100644
--- a/drivers/cpuidle/coupled.c
+++ b/drivers/cpuidle/coupled.c
@@ -130,6 +130,43 @@ 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
* @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_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 *
******************************/
--
1.7.12.rc0