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authorPeter Zijlstra <a.p.zijlstra@chello.nl>2011-04-05 10:14:25 +0200
committerIngo Molnar <mingo@elte.hu>2011-04-05 10:29:36 +0200
commit49c022e657fbe661460d191fbe776a387132e2b3 (patch)
tree487b713816a5ff3d81437aeecf111ffa414f6ede /kernel
parentb2a8b4b81966094703088a7bc76a313af841924d (diff)
sched: Clean up rebalance_domains() load-balance interval calculation
Instead of the possible multiple-evaluation of num_online_cpus() in rebalance_domains() that Linus reported, avoid it altogether in the normal case since it's implemented with a Hamming weight function over a cpu bitmask which can be darn expensive for those with big iron. This also makes it cleaner, smaller and documents the code. Reported-by: Linus Torvalds <torvalds@linux-foundation.org> Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl> LKML-Reference: <1301991265.2225.12.camel@twins> Signed-off-by: Ingo Molnar <mingo@elte.hu>
Diffstat (limited to 'kernel')
-rw-r--r--kernel/sched.c3
-rw-r--r--kernel/sched_fair.c16
2 files changed, 15 insertions, 4 deletions
diff --git a/kernel/sched.c b/kernel/sched.c
index a8845516ace6..17b4d226ee0d 100644
--- a/kernel/sched.c
+++ b/kernel/sched.c
@@ -6331,6 +6331,9 @@ migration_call(struct notifier_block *nfb, unsigned long action, void *hcpu)
break;
#endif
}
+
+ update_max_interval();
+
return NOTIFY_OK;
}
diff --git a/kernel/sched_fair.c b/kernel/sched_fair.c
index c7ec5c8e7b44..80ecd09452e0 100644
--- a/kernel/sched_fair.c
+++ b/kernel/sched_fair.c
@@ -3820,6 +3820,17 @@ void select_nohz_load_balancer(int stop_tick)
static DEFINE_SPINLOCK(balancing);
+static unsigned long __read_mostly max_load_balance_interval = HZ/10;
+
+/*
+ * Scale the max load_balance interval with the number of CPUs in the system.
+ * This trades load-balance latency on larger machines for less cross talk.
+ */
+static void update_max_interval(void)
+{
+ max_load_balance_interval = HZ*num_online_cpus()/10;
+}
+
/*
* It checks each scheduling domain to see if it is due to be balanced,
* and initiates a balancing operation if so.
@@ -3849,10 +3860,7 @@ static void rebalance_domains(int cpu, enum cpu_idle_type idle)
/* scale ms to jiffies */
interval = msecs_to_jiffies(interval);
- if (unlikely(!interval))
- interval = 1;
- if (interval > HZ*num_online_cpus()/10)
- interval = HZ*num_online_cpus()/10;
+ interval = clamp(interval, 1UL, max_load_balance_interval);
need_serialize = sd->flags & SD_SERIALIZE;

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