mutex: preemption fixes
The problem is that dropping the spinlock right before schedule is a voluntary
preemption point and can cause a schedule, right after which we schedule again.
Fix this inefficiency by keeping preemption disabled until we schedule, do this
by explicity disabling preemption and providing a schedule() variant that
assumes preemption is already disabled.
Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
diff --git a/kernel/sched.c b/kernel/sched.c
index 8be2c13..b001c13 100644
--- a/kernel/sched.c
+++ b/kernel/sched.c
@@ -4538,15 +4538,13 @@
/*
* schedule() is the main scheduler function.
*/
-asmlinkage void __sched schedule(void)
+asmlinkage void __sched __schedule(void)
{
struct task_struct *prev, *next;
unsigned long *switch_count;
struct rq *rq;
int cpu;
-need_resched:
- preempt_disable();
cpu = smp_processor_id();
rq = cpu_rq(cpu);
rcu_qsctr_inc(cpu);
@@ -4603,7 +4601,13 @@
if (unlikely(reacquire_kernel_lock(current) < 0))
goto need_resched_nonpreemptible;
+}
+asmlinkage void __sched schedule(void)
+{
+need_resched:
+ preempt_disable();
+ __schedule();
preempt_enable_no_resched();
if (unlikely(test_thread_flag(TIF_NEED_RESCHED)))
goto need_resched;
