[PATCH 1/2] sched/isolation: Add cpu_is_isolated() API

[Michal Hocko]

From: Frederic Weisbecker <frederic@xxxxxxxxxx>

Provide this new API to check if a CPU has been isolated either through
isolcpus= or nohz_full= kernel parameter.

It aims at avoiding kernel load deemed to be safely spared on CPUs
running sensitive workload that can't bear any disturbance, such as
pcp cache draining.

Suggested-by: Michal Hocko <mhocko@xxxxxxxx>
Signed-off-by: Frederic Weisbecker <frederic@xxxxxxxxxx>
Signed-off-by: Michal Hocko <mhocko@xxxxxxxx>
---
 include/linux/sched/isolation.h | 12 ++++++++++++
 1 file changed, 12 insertions(+)

diff --git a/include/linux/sched/isolation.h b/include/linux/sched/isolation.h
index 8c15abd67aed..fe1a46f30d24 100644
--- a/include/linux/sched/isolation.h
+++ b/include/linux/sched/isolation.h
@@ -46,6 +46,12 @@ static inline bool housekeeping_enabled(enum hk_type type)
 
 static inline void housekeeping_affine(struct task_struct *t,
 				       enum hk_type type) { }
+
+static inline bool housekeeping_test_cpu(int cpu, enum hk_type type)
+{
+	return true;
+}
+
 static inline void housekeeping_init(void) { }
 #endif /* CONFIG_CPU_ISOLATION */
 
@@ -58,4 +64,10 @@ static inline bool housekeeping_cpu(int cpu, enum hk_type type)
 	return true;
 }
 
+static inline bool cpu_is_isolated(int cpu)
+{
+	return !housekeeping_test_cpu(cpu, HK_TYPE_DOMAIN) ||
+		 !housekeeping_test_cpu(cpu, HK_TYPE_TICK);
+}
+
 #endif /* _LINUX_SCHED_ISOLATION_H */
-- 
2.30.2