perf: New helper to prevent full dynticks CPUs from stopping tick

Provide a new helper that help full dynticks CPUs to prevent
from stopping their tick in case there are events in the local
rotation list.

This way we make sure that perf_event_task_tick() is serviced
on demand.

Signed-off-by: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Chris Metcalf <cmetcalf@tilera.com>
Cc: Christoph Lameter <cl@linux.com>
Cc: Geoff Levand <geoff@infradead.org>
Cc: Gilad Ben Yossef <gilad@benyossef.com>
Cc: Hakan Akkan <hakanakkan@gmail.com>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Kevin Hilman <khilman@linaro.org>
Cc: Li Zhong <zhong@linux.vnet.ibm.com>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: Paul Gortmaker <paul.gortmaker@windriver.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Stephane Eranian <eranian@google.com>
Cc: Jiri Olsa <jolsa@redhat.com>

diff --git a/include/linux/perf_event.h b/include/linux/perf_event.h
index e47ee462c2f2e69a8cbef4ef3a3d7bfc873cb51f..0140830225e216103742f1dc1f6736d461f86d8a 100644 (file)
--- a/include/linux/perf_event.h
+++ b/include/linux/perf_event.h
@@ -799,6 +799,12 @@ static inline int __perf_event_disable(void *info)                 { return -1; }
 static inline void perf_event_task_tick(void)                          { }
 #endif
 
+#if defined(CONFIG_PERF_EVENTS) && defined(CONFIG_NO_HZ_FULL)
+extern bool perf_event_can_stop_tick(void);
+#else
+static inline bool perf_event_can_stop_tick(void)                      { return true; }
+#endif
+
 #define perf_output_put(handle, x) perf_output_copy((handle), &(x), sizeof(x))
 
 /*

diff --git a/kernel/events/core.c b/kernel/events/core.c
index 75b58bb75b328cf7560fd8851ccc09d822158967..ddb993b52190e9504b2b4505ec263034eb65801c 100644 (file)
--- a/kernel/events/core.c
+++ b/kernel/events/core.c
@@ -2560,6 +2560,16 @@ done:
                list_del_init(&cpuctx->rotation_list);
 }
 
+#ifdef CONFIG_NO_HZ_FULL
+bool perf_event_can_stop_tick(void)
+{
+       if (list_empty(&__get_cpu_var(rotation_list)))
+               return true;
+       else
+               return false;
+}
+#endif
+
 void perf_event_task_tick(void)
 {
        struct list_head *head = &__get_cpu_var(rotation_list);