[PATCH 07/10] nohz: Implement full dynticks kick

Frederic Weisbecker
2013-04-22T19:00:10Z

Implement the full dynticks kick that is performed from
IPIs sent by various subsystems (scheduler, posix timers, ...)
when they want to notify about a new event that may
reconsider the dependency on the tick.

Most of the time, such an event end up restarting the tick.

(Part of the design with subsystems providing *_can_stop_tick()
helpers suggested by Peter Zijlstra a while ago).

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>
---
kernel/time/tick-sched.c | 42 ++++++++++++++++++++++++++++++++++++++----
1 files changed, 38 insertions(+), 4 deletions(-)

diff --git a/kernel/time/tick-sched.c b/kernel/time/tick-sched.c
index 4d74a68..95d79ae 100644
--- a/kernel/time/tick-sched.c
+++ b/kernel/time/tick-sched.c
@@ -21,6 +21,8 @@
#include <linux/sched.h>
#include <linux/module.h>
#include <linux/irq_work.h>
+#include <linux/posix-timers.h>
+#include <linux/perf_event.h>

#include <asm/irq_regs.h>

@@ -147,16 +149,48 @@ static void tick_sched_handle(struct tick_sched *ts, struct pt_regs *regs)
static cpumask_var_t nohz_full_mask;
bool have_nohz_full_mask;

+static bool can_stop_full_tick(void)
+{
+ WARN_ON_ONCE(!irqs_disabled());
+
+ if (!sched_can_stop_tick())
+ return false;
+
+ if (!posix_cpu_timers_can_stop_tick(current))
+ return false;
+
+ if (!perf_event_can_stop_tick())
+ return false;
+
+ /* sched_clock_tick() needs us? */
+#ifdef CONFIG_HAVE_UNSTABLE_SCHED_CLOCK
+ /*
+ * TODO: kick full dynticks CPUs when
+ * sched_clock_stable is set.
+ */
+ if (!sched_clock_stable)
+ return false;
+#endif
+
+ return true;
+}
+
+static void tick_nohz_restart_sched_tick(struct tick_sched *ts, ktime_t now);
+
/*
* Re-evaluate the need for the tick on the current CPU
* and restart it if necessary.
*/
void tick_nohz_full_check(void)
{
- /*
- * STUB for now, will be filled with the full tick stop/restart
- * infrastructure patches
- */
+ struct tick_sched *ts = &__get_cpu_var(tick_cpu_sched);
+
+ if (tick_nohz_full_cpu(smp_processor_id())) {
+ if (ts->tick_stopped && !is_idle_task(current)) {
+ if (!can_stop_full_tick())
+ tick_nohz_restart_sched_tick(ts, ktime_get());
+ }
+ }
}

static void nohz_full_kick_work_func(struct irq_work *work)
--
1.7.5.4