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authorPeter Zijlstra <a.p.zijlstra@chello.nl>2011-04-05 04:14:25 -0400
committerIngo Molnar <mingo@elte.hu>2011-04-05 04:29:36 -0400
commit49c022e657fbe661460d191fbe776a387132e2b3 (patch)
tree487b713816a5ff3d81437aeecf111ffa414f6ede /kernel/sched_fair.c
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/sched_fair.c')
-rw-r--r--kernel/sched_fair.c16
1 files changed, 12 insertions, 4 deletions
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)
3820 3820
3821static DEFINE_SPINLOCK(balancing); 3821static DEFINE_SPINLOCK(balancing);
3822 3822
3823static unsigned long __read_mostly max_load_balance_interval = HZ/10;
3824
3825/*
3826 * Scale the max load_balance interval with the number of CPUs in the system.
3827 * This trades load-balance latency on larger machines for less cross talk.
3828 */
3829static void update_max_interval(void)
3830{
3831 max_load_balance_interval = HZ*num_online_cpus()/10;
3832}
3833
3823/* 3834/*
3824 * It checks each scheduling domain to see if it is due to be balanced, 3835 * It checks each scheduling domain to see if it is due to be balanced,
3825 * and initiates a balancing operation if so. 3836 * and initiates a balancing operation if so.
@@ -3849,10 +3860,7 @@ static void rebalance_domains(int cpu, enum cpu_idle_type idle)
3849 3860
3850 /* scale ms to jiffies */ 3861 /* scale ms to jiffies */
3851 interval = msecs_to_jiffies(interval); 3862 interval = msecs_to_jiffies(interval);
3852 if (unlikely(!interval)) 3863 interval = clamp(interval, 1UL, max_load_balance_interval);
3853 interval = 1;
3854 if (interval > HZ*num_online_cpus()/10)
3855 interval = HZ*num_online_cpus()/10;
3856 3864
3857 need_serialize = sd->flags & SD_SERIALIZE; 3865 need_serialize = sd->flags & SD_SERIALIZE;
3858 3866