From: Peter Zijlstra <peterz@infradead.org>
Date: Mon, 19 Sep 2016 10:57:53 +0000 (+0200)
Subject: sched/core: Avoid _cond_resched() for PREEMPT=y
X-Git-Tag: v4.9-rc1~162^2~27
X-Git-Url: https://git.karo-electronics.de/?a=commitdiff_plain;h=35a773a07926a22bf19d77ee00024522279c4e68;p=karo-tx-linux.git

sched/core: Avoid _cond_resched() for PREEMPT=y

On fully preemptible kernels _cond_resched() is pointless, so avoid
emitting any code for it.

Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Mikulas Patocka <mpatocka@redhat.com>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: linux-kernel@vger.kernel.org
Signed-off-by: Ingo Molnar <mingo@kernel.org>
---

diff --git a/include/linux/sched.h b/include/linux/sched.h
index f00ee8e90a29..b99fcd1b341e 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -3209,7 +3209,11 @@ static inline int signal_pending_state(long state, struct task_struct *p)
  * cond_resched_lock() will drop the spinlock before scheduling,
  * cond_resched_softirq() will enable bhs before scheduling.
  */
+#ifndef CONFIG_PREEMPT
 extern int _cond_resched(void);
+#else
+static inline int _cond_resched(void) { return 0; }
+#endif
 
 #define cond_resched() ({			\
 	___might_sleep(__FILE__, __LINE__, 0);	\
diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index b2ec53c1a974..d7babcc7cb76 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -4883,6 +4883,7 @@ SYSCALL_DEFINE0(sched_yield)
 	return 0;
 }
 
+#ifndef CONFIG_PREEMPT
 int __sched _cond_resched(void)
 {
 	if (should_resched(0)) {
@@ -4892,6 +4893,7 @@ int __sched _cond_resched(void)
 	return 0;
 }
 EXPORT_SYMBOL(_cond_resched);
+#endif
 
 /*
  * __cond_resched_lock() - if a reschedule is pending, drop the given lock,