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On Wed, May 01, 2013 at 05:22:05PM +0300, Julian Anastasov wrote:
> > static void inline cond_resched_rcu_lock(void)
> > {
> > #ifdef CONFIG_PREEMPT_RCU
>
> You mean '#ifndef' here, right? But in the non-preempt
> case is using the need_resched() needed? rcu_read_unlock
> and rcu_read_lock do not generate code.
Uhm... yes!
> > if (need_resched()) {
> > rcu_read_unlock();
> > cond_resched();
> > rcu_read_lock();
> > }
> > #endif /* CONFIG_PREEMPT_RCU */
> > }
> >
> > That would have an rcu_read_lock() break and voluntary preemption point for
> > non-preemptible RCU and not bother with the stuff for preemptible RCU.
>
> I see. So, can we choose one of both variants:
>
> 1. Your variant but with ifndef:
>
> static void inline cond_resched_rcu_lock(void)
> {
> #ifndef CONFIG_PREEMPT_RCU
> if (need_resched()) {
> rcu_read_unlock();
> cond_resched();
> rcu_read_lock();
> }
> #endif
> }
>
> 2. Same without need_resched because cond_resched already
> performs the same checks:
>
> static void inline cond_resched_rcu_lock(void)
> {
> #ifndef CONFIG_PREEMPT_RCU
> rcu_read_unlock();
> cond_resched();
> rcu_read_lock();
> #endif
> }
Ah so the 'problem' with this last version is that it does an unconditional /
unnessecary rcu_read_unlock().
The below would be in line with all the other cond_resched*() implementations.
---
include/linux/sched.h | 7 +++++++
kernel/sched/core.c | 14 ++++++++++++++
2 files changed, 21 insertions(+)
diff --git a/include/linux/sched.h b/include/linux/sched.h
index 802a751..fd2c77f 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -2449,6 +2449,13 @@ extern int __cond_resched_softirq(void);
__cond_resched_softirq(); \
})
+extern int __cond_resched_rcu(void);
+
+#define cond_resched_rcu() ({ \
+ __might_sleep(__FILE__, __LINE__, 0); \
+ __cond_resched_rcu(); \
+})
+
/*
* Does a critical section need to be broken due to another
* task waiting?: (technically does not depend on CONFIG_PREEMPT,
diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index 7d7901a..2b3b4e6 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -4358,6 +4358,20 @@ int __sched __cond_resched_softirq(void)
}
EXPORT_SYMBOL(__cond_resched_softirq);
+int __sched __cond_resched_rcu(void)
+{
+#ifndef CONFIG_PREEMPT_RCU
+ if (should_resched()) {
+ rcu_read_unlock();
+ __cond_resched();
+ rcu_read_lock();
+ return 1;
+ }
+#endif
+ return 0;
+}
+EXPORT_SYMBOL(__cond_resched_rcu);
+
/**
* yield - yield the current processor to other threads.
*
--
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