[PATCH] sched: add option to serialize load balancing

Large sched domains can be very expensive to scan.  Add an option SD_SERIALIZE
to the sched domain flags.  If that flag is set then we make sure that no
other such domain is being balanced.

[akpm@osdl.org: build fix]
Signed-off-by: Christoph Lameter <clameter@sgi.com>
Cc: Peter Williams <pwil3058@bigpond.net.au>
Cc: Nick Piggin <nickpiggin@yahoo.com.au>
Cc: Christoph Lameter <clameter@sgi.com>
Cc: "Siddha, Suresh B" <suresh.b.siddha@intel.com>
Cc: "Chen, Kenneth W" <kenneth.w.chen@intel.com>
Acked-by: Ingo Molnar <mingo@elte.hu>
Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

1 files changed, 9 insertions, 0 deletions

diff --git a/kernel/sched.c b/kernel/sched.c
index 0a4a26b21f69..2b2b780939c9 100644
--- a/kernel/sched.c
+++ b/kernel/sched.c
@@ -2880,6 +2880,7 @@ static void update_load(struct rq *this_rq)
  *
  * Balancing parameters are set up in arch_init_sched_domains.
  */
+static DEFINE_SPINLOCK(balancing);
 
 static void run_rebalance_domains(struct softirq_action *h)
 {
@@ -2909,6 +2910,11 @@ static void run_rebalance_domains(struct softirq_action *h)
                 if (unlikely(!interval))
                         interval = 1;
 
+                if (sd->flags & SD_SERIALIZE) {
+                        if (!spin_trylock(&balancing))
+                                goto out;
+                }
+
                 if (time_after_eq(jiffies, sd->last_balance + interval)) {
                         if (load_balance(this_cpu, this_rq, sd, idle)) {
                                 /*
@@ -2920,6 +2926,9 @@ static void run_rebalance_domains(struct softirq_action *h)
                         }
                         sd->last_balance = jiffies;
                 }
+                if (sd->flags & SD_SERIALIZE)
+                        spin_unlock(&balancing);
+out:
                 if (time_after(next_balance, sd->last_balance + interval))
                         next_balance = sd->last_balance + interval;
         }