sched/nohz: Fix affine unpinned timers mess

The following commit:

  9642d18eee2c ("nohz: Affine unpinned timers to housekeepers")'

intended to affine unpinned timers to housekeepers:

  unpinned timers(full dynaticks, idle)   =>   nearest busy housekeepers(otherwise, fallback to any housekeepers)
  unpinned timers(full dynaticks, busy)   =>   nearest busy housekeepers(otherwise, fallback to any housekeepers)
  unpinned timers(houserkeepers, idle)    =>   nearest busy housekeepers(otherwise, fallback to itself)

However, the !idle_cpu(i) && is_housekeeping_cpu(cpu) check modified the
intention to:

  unpinned timers(full dynaticks, idle)   =>   any housekeepers(no mattter cpu topology)
  unpinned timers(full dynaticks, busy)   =>   any housekeepers(no mattter cpu topology)
  unpinned timers(housekeepers, idle)     =>   any busy cpus(otherwise, fallback to any housekeepers)

This patch fixes it by checking if there are busy housekeepers nearby,
otherwise falls to any housekeepers/itself. After the patch:

  unpinned timers(full dynaticks, idle)   =>   nearest busy housekeepers(otherwise, fallback to any housekeepers)
  unpinned timers(full dynaticks, busy)   =>   nearest busy housekeepers(otherwise, fallback to any housekeepers)
  unpinned timers(housekeepers, idle)     =>   nearest busy housekeepers(otherwise, fallback to itself)

Signed-off-by: Wanpeng Li <[email protected]>
Signed-off-by: Peter Zijlstra (Intel) <[email protected]>
[ Fixed the changelog. ]
Cc: Frederic Weisbecker <[email protected]>
Cc: Linus Torvalds <[email protected]>
Cc: Mike Galbraith <[email protected]>
Cc: Peter Zijlstra <[email protected]>
Cc: Thomas Gleixner <[email protected]>
Cc: [email protected]
Fixes: 'commit 9642d18eee2c ("nohz: Affine unpinned timers to housekeepers")'
Link: http://lkml.kernel.org/r/[email protected]
Signed-off-by: Ingo Molnar <[email protected]>

diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index 636c4b9cac38037a08407f7bf96faac2427825af..6f6962a356b49717b2f15337ace634bf498145f7 100644 (file)
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -533,7 +533,10 @@ int get_nohz_timer_target(void)
        rcu_read_lock();
        for_each_domain(cpu, sd) {
                for_each_cpu(i, sched_domain_span(sd)) {
-                       if (!idle_cpu(i) && is_housekeeping_cpu(cpu)) {
+                       if (cpu == i)
+                               continue;
+
+                       if (!idle_cpu(i) && is_housekeeping_cpu(i)) {
                                cpu = i;
                                goto unlock;
                        }