smp: Introduce a helper function to check for pending IPIs

When governors used during cpuidle try to find the most optimal idle state
for a CPU or a group of CPUs, they are known to quite often fail. One
reason for this is, that they are not taking into account whether there has
been an IPI scheduled for any of the CPUs that are affected by the selected
idle state.

To enable pending IPIs to be taken into account for cpuidle decisions,
introduce a new helper function, cpus_peek_for_pending_ipi().

Suggested-by: Thomas Gleixner <tglx@linutronix.de>
Reviewed-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>

1 files changed, 22 insertions, 0 deletions

diff --git a/kernel/smp.c b/kernel/smp.c
index 02f52291fae4..f349960f79ca 100644
--- a/kernel/smp.c
+++ b/kernel/smp.c
@@ -1088,6 +1088,28 @@ void wake_up_all_idle_cpus(void)
 EXPORT_SYMBOL_GPL(wake_up_all_idle_cpus);
 
 /**
+ * cpus_peek_for_pending_ipi - Check for pending IPI for CPUs
+ * @mask: The CPU mask for the CPUs to check.
+ *
+ * This function walks through the @mask to check if there are any pending IPIs
+ * scheduled, for any of the CPUs in the @mask. It does not guarantee
+ * correctness as it only provides a racy snapshot.
+ *
+ * Returns true if there is a pending IPI scheduled and false otherwise.
+ */
+bool cpus_peek_for_pending_ipi(const struct cpumask *mask)
+{
+	unsigned int cpu;
+
+	for_each_cpu(cpu, mask) {
+		if (!llist_empty(per_cpu_ptr(&call_single_queue, cpu)))
+			return true;
+	}
+
+	return false;
+}
+
+/**
  * struct smp_call_on_cpu_struct - Call a function on a specific CPU
  * @work: &work_struct
  * @done: &completion to signal