[PATCH 03/10] perf: New helper to prevent full dynticks CPUs from stopping tick

Frederic Weisbecker
2013-04-22T19:00:03Z

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>
---
include/linux/perf_event.h | 6 ++++++
kernel/events/core.c | 10 ++++++++++
2 files changed, 16 insertions(+), 0 deletions(-)

diff --git a/include/linux/perf_event.h b/include/linux/perf_event.h
index e47ee46..0140830 100644
--- 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 75b58bb..ddb993b 100644
--- 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);
--
1.7.5.4