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From 708dbc824657476807e387253001204df09c25ee Mon Sep 17 00:00:00 2001
From: Peter Zijlstra <peterz@infradead.org>
Date: Tue, 16 Mar 2010 14:31:44 -0700
Subject: [PATCH] sched: Break out from load_balancing on rq_lock contention
commit 5d2740b70e7f6ad29104aec72956fb6e4d143809 in tip.
[PG: account for sched --> sched_fair code moves and that
the lock break in move_tasks is now upstream as baa8c110]
Signed-off-by: Peter Zijlstra <peterz@infradead.org>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Paul Gortmaker <paul.gortmaker@windriver.com>
---
kernel/sched.c | 4 ++++
kernel/sched_fair.c | 18 ++++++++++++++++++
2 files changed, 22 insertions(+), 0 deletions(-)
diff --git a/kernel/sched.c b/kernel/sched.c
index 46869d9..e94915f 100644
--- a/kernel/sched.c
+++ b/kernel/sched.c
@@ -824,7 +824,11 @@ late_initcall(sched_init_debug);
* Number of tasks to iterate in a single balance run.
* Limited because this is done with IRQs disabled.
*/
+#ifndef CONFIG_PREEMPT
const_debug unsigned int sysctl_sched_nr_migrate = 32;
+#else
+const_debug unsigned int sysctl_sched_nr_migrate = 8;
+#endif
/*
* ratelimit for updating the group shares.
diff --git a/kernel/sched_fair.c b/kernel/sched_fair.c
index add5302..f776fff 100644
--- a/kernel/sched_fair.c
+++ b/kernel/sched_fair.c
@@ -1954,6 +1954,10 @@ balance_tasks(struct rq *this_rq, int this_cpu, struct rq *busiest,
*/
if (idle == CPU_NEWLY_IDLE)
break;
+
+ if (raw_spin_is_contended(&this_rq->lock) ||
+ raw_spin_is_contended(&busiest->lock))
+ break;
#endif
/*
@@ -2022,6 +2026,20 @@ load_balance_fair(struct rq *this_rq, int this_cpu, struct rq *busiest,
rem_load_move -= moved_load;
if (rem_load_move < 0)
break;
+
+#ifdef CONFIG_PREEMPT
+ /*
+ * NEWIDLE balancing is a source of latency, so preemptible
+ * kernels will stop after the first task is pulled to minimize
+ * the critical section.
+ */
+ if (idle == CPU_NEWLY_IDLE && this_rq->nr_running)
+ break;
+
+ if (raw_spin_is_contended(&this_rq->lock) ||
+ raw_spin_is_contended(&busiest->lock))
+ break;
+#endif
}
rcu_read_unlock();
--
1.7.0.4
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