Commit-ID: 49c022e657fbe661460d191fbe776a387132e2b3
Gitweb: http://git.kernel.org/tip/49c022e657fbe661460d191fbe776a387132e2b3
Author: Peter Zijlstra <a.p.zijlstra@xxxxxxxxx>
AuthorDate: Tue, 5 Apr 2011 10:14:25 +0200
Committer: Ingo Molnar <mingo@xxxxxxx>
CommitDate: Tue, 5 Apr 2011 10:29:36 +0200
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@xxxxxxxxxxxxxxxxxxxx>
Signed-off-by: Peter Zijlstra <a.p.zijlstra@xxxxxxxxx>
LKML-Reference: <1301991265.2225.12.camel@twins>
Signed-off-by: Ingo Molnar <mingo@xxxxxxx>
---
kernel/sched.c | 3 +++
kernel/sched_fair.c | 16 ++++++++++++----
2 files changed, 15 insertions(+), 4 deletions(-)
diff --git a/kernel/sched.c b/kernel/sched.c
index a884551..17b4d22 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 c7ec5c8..80ecd09 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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