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| author | Peter Zijlstra <a.p.zijlstra@chello.nl> | 2011-04-05 10:14:25 +0200 |
|---|---|---|
| committer | Ingo Molnar <mingo@elte.hu> | 2011-04-05 10:29:36 +0200 |
| commit | 49c022e657fbe661460d191fbe776a387132e2b3 (patch) | |
| tree | 487b713816a5ff3d81437aeecf111ffa414f6ede /kernel | |
| parent | b2a8b4b81966094703088a7bc76a313af841924d (diff) | |
| download | lwn-49c022e657fbe661460d191fbe776a387132e2b3.tar.gz lwn-49c022e657fbe661460d191fbe776a387132e2b3.zip | |
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.c | 3 | ||||
| -rw-r--r-- | kernel/sched_fair.c | 16 |
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; |