nohz: Affine unpinned timers to housekeepers

The problem addressed in this patch is about affining unpinned
timers. Adaptive or Full Dynticks CPUs are currently disturbed
by unnecessary jitter due to firing of such timers on them.

This patch will affine timers to online CPUs which are not full
dynticks in NOHZ_FULL configured systems. It should not
introduce overhead in nohz full off case due to static keys.

Signed-off-by: Vatika Harlalka <vatikaharlalka@gmail.com>
Signed-off-by: Frederic Weisbecker <fweisbec@gmail.com>
Reviewed-by: Preeti U Murthy <preeti@linux.vnet.ibm.com>
Acked-by: Thomas Gleixner <tglx@linutronix.de>
Cc: Chris Metcalf <cmetcalf@ezchip.com>
Cc: Christoph Lameter <cl@linux.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Link: http://lkml.kernel.org/r/1441119060-2230-2-git-send-email-fweisbec@gmail.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>

1 files changed, 5 insertions, 2 deletions

diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index 8b864ecee0e1..0902e4d72671 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -623,18 +623,21 @@ int get_nohz_timer_target(void)
         int i, cpu = smp_processor_id();
         struct sched_domain *sd;
 
-        if (!idle_cpu(cpu))
+        if (!idle_cpu(cpu) && is_housekeeping_cpu(cpu))
                 return cpu;
 
         rcu_read_lock();
         for_each_domain(cpu, sd) {
                 for_each_cpu(i, sched_domain_span(sd)) {
-                        if (!idle_cpu(i)) {
+                        if (!idle_cpu(i) && is_housekeeping_cpu(cpu)) {
                                 cpu = i;
                                 goto unlock;
                         }
                 }
         }
+
+        if (!is_housekeeping_cpu(cpu))
+                cpu = housekeeping_any_cpu();
 unlock:
         rcu_read_unlock();
         return cpu;