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authorSuresh Siddha <suresh.b.siddha@intel.com>2009-02-04 11:59:44 -0800
committerIngo Molnar <mingo@elte.hu>2009-02-04 22:31:19 +0100
commit483b4ee60edbefdfbff0dd538fb81f368d9e7c0d (patch)
tree2fbf152e6bb6377a16a1fb0d1aa503d19e0c0f63 /kernel
parent35626129abcd6a7547e84c817ef5b6eff7a8758b (diff)
downloadop-kernel-dev-483b4ee60edbefdfbff0dd538fb81f368d9e7c0d.zip
op-kernel-dev-483b4ee60edbefdfbff0dd538fb81f368d9e7c0d.tar.gz
sched: fix nohz load balancer on cpu offline
Christian Borntraeger reports: > After a logical cpu offline, even on a complete idle system, there > is one cpu with full ticks. It turns out that nohz.cpu_mask has the > the offlined cpu still set. > > In select_nohz_load_balancer() we check if the system is completely > idle to turn of load balancing. We compare cpu_online_map with > nohz.cpu_mask. Since cpu_online_map is updated on cpu unplug, > but nohz.cpu_mask is not, the check fails and the scheduler believes > that we need an "idle load balancer" even on a fully idle system. > Since the ilb cpu does not deactivate the timer tick this breaks NOHZ. Fix the select_nohz_load_balancer() to not set the nohz.cpu_mask while a cpu is going offline. Reported-by: Christian Borntraeger <borntraeger@de.ibm.com> Signed-off-by: Suresh Siddha <suresh.b.siddha@intel.com> Tested-by: Christian Borntraeger <borntraeger@de.ibm.com> Signed-off-by: Ingo Molnar <mingo@elte.hu>
Diffstat (limited to 'kernel')
-rw-r--r--kernel/sched.c17
1 files changed, 11 insertions, 6 deletions
diff --git a/kernel/sched.c b/kernel/sched.c
index 242d0d4..e1fc67d 100644
--- a/kernel/sched.c
+++ b/kernel/sched.c
@@ -3890,19 +3890,24 @@ int select_nohz_load_balancer(int stop_tick)
int cpu = smp_processor_id();
if (stop_tick) {
- cpumask_set_cpu(cpu, nohz.cpu_mask);
cpu_rq(cpu)->in_nohz_recently = 1;
- /*
- * If we are going offline and still the leader, give up!
- */
- if (!cpu_active(cpu) &&
- atomic_read(&nohz.load_balancer) == cpu) {
+ if (!cpu_active(cpu)) {
+ if (atomic_read(&nohz.load_balancer) != cpu)
+ return 0;
+
+ /*
+ * If we are going offline and still the leader,
+ * give up!
+ */
if (atomic_cmpxchg(&nohz.load_balancer, cpu, -1) != cpu)
BUG();
+
return 0;
}
+ cpumask_set_cpu(cpu, nohz.cpu_mask);
+
/* time for ilb owner also to sleep */
if (cpumask_weight(nohz.cpu_mask) == num_online_cpus()) {
if (atomic_read(&nohz.load_balancer) == cpu)
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