timer: Don't run non-pinned timer to full dynticks CPUs
While trying to find a target for a non-pinned timer, use
the following logic:
- Use the closest (from a sched domain POV) busy CPU that
is not full dynticks
- If none, use the closest idle CPU that is not full dynticks.
So this is biased toward isolation over powersaving. This is
a quick hack until we provide a way for the user to tune that
policy. A CPU mask affinity for non pinned timers could be such
a solution.
Original-patch-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Alessio Igor Bogani <abogani@kernel.org>
Cc: Andrew Morton <akpm@linux-foundation.org>
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: 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>
diff --git a/kernel/hrtimer.c b/kernel/hrtimer.c
index 6db7a5e..f5da6fb 100644
--- a/kernel/hrtimer.c
+++ b/kernel/hrtimer.c
@@ -159,7 +159,8 @@
static int hrtimer_get_target(int this_cpu, int pinned)
{
#ifdef CONFIG_NO_HZ
- if (!pinned && get_sysctl_timer_migration() && idle_cpu(this_cpu))
+ if (!pinned && get_sysctl_timer_migration() &&
+ (idle_cpu(this_cpu) || tick_nohz_full_cpu(this_cpu)))
return get_nohz_timer_target();
#endif
return this_cpu;
diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index 7b6156a..e2884c5 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -560,22 +560,42 @@
*/
int get_nohz_timer_target(void)
{
- int cpu = smp_processor_id();
int i;
struct sched_domain *sd;
+ int cpu = smp_processor_id();
+ int target = -1;
rcu_read_lock();
for_each_domain(cpu, sd) {
for_each_cpu(i, sched_domain_span(sd)) {
+ /*
+ * This is biased toward CPU isolation usecase:
+ * try to migrate the timer to a busy non-full-nohz
+ * CPU. If there is none, then prefer an idle CPU
+ * than a full nohz one.
+ * We shouldn't do policy here (isolation VS powersaving)
+ * so this is a temporary hack. Being able to affine
+ * non-pinned timers would be a better thing.
+ */
+ if (tick_nohz_full_cpu(i))
+ continue;
+
if (!idle_cpu(i)) {
- cpu = i;
+ target = i;
goto unlock;
}
+
+ if (target == -1)
+ target = i;
}
}
+ /* Fallback in case of NULL domain */
+ if (target == -1)
+ target = cpu;
unlock:
rcu_read_unlock();
- return cpu;
+
+ return target;
}
/*
* When add_timer_on() enqueues a timer into the timer wheel of an
diff --git a/kernel/timer.c b/kernel/timer.c
index 970b57d..51dd02b 100644
--- a/kernel/timer.c
+++ b/kernel/timer.c
@@ -738,7 +738,8 @@
cpu = smp_processor_id();
#if defined(CONFIG_NO_HZ) && defined(CONFIG_SMP)
- if (!pinned && get_sysctl_timer_migration() && idle_cpu(cpu))
+ if (!pinned && get_sysctl_timer_migration() &&
+ (idle_cpu(cpu) || tick_nohz_full_cpu(cpu)))
cpu = get_nohz_timer_target();
#endif
new_base = per_cpu(tvec_bases, cpu);
