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DateFri, 13 Mar 2009 12:21:26 +0100
FromPeter Zijlstra <>
Subject[PATCH 01/11] sched: remove extra call overhead for schedule()
Lai Jiangshan's patch reminded me that I promised Nick to remove that
extra call overhead in schedule().

Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
---
kernel/mutex.c | 4 +++-
kernel/sched.c | 12 ++++--------
2 files changed, 7 insertions(+), 9 deletions(-)
Index: linux-2.6/kernel/mutex.c
===================================================================
--- linux-2.6.orig/kernel/mutex.c
+++ linux-2.6/kernel/mutex.c
@@ -248,7 +248,9 @@ __mutex_lock_common(struct mutex *lock,

/* didnt get the lock, go to sleep: */
spin_unlock_mutex(&lock->wait_lock, flags);
- __schedule();
+ preempt_enable_no_resched();
+ schedule();
+ preempt_disable();
spin_lock_mutex(&lock->wait_lock, flags);
}

Index: linux-2.6/kernel/sched.c
===================================================================
--- linux-2.6.orig/kernel/sched.c
+++ linux-2.6/kernel/sched.c
@@ -4763,13 +4763,15 @@ pick_next_task(struct rq *rq)
/*
* 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);
@@ -4827,15 +4829,9 @@ need_resched_nonpreemptible:

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)))
+ if (need_resched())
goto need_resched;
}
EXPORT_SYMBOL(schedule);
--



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