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authorPaul E. McKenney <paulmck@linux.vnet.ibm.com>2014-07-01 22:26:57 +0400
committerPaul E. McKenney <paulmck@linux.vnet.ibm.com>2014-09-08 03:27:20 +0400
commitbde6c3aa993066acb0d6ce32ecabe03b9d5df92d (patch)
tree09ec78a9cfa751ce36288c32c4e5112f34af8582 /include/linux/rcupdate.h
parent8315f42295d2667a7f942f154b73a86fd7cb2227 (diff)
downloadlinux-bde6c3aa993066acb0d6ce32ecabe03b9d5df92d.tar.xz
rcu: Provide cond_resched_rcu_qs() to force quiescent states in long loops
RCU-tasks requires the occasional voluntary context switch from CPU-bound in-kernel tasks. In some cases, this requires instrumenting cond_resched(). However, there is some reluctance to countenance unconditionally instrumenting cond_resched() (see http://lwn.net/Articles/603252/), so this commit creates a separate cond_resched_rcu_qs() that may be used in place of cond_resched() in locations prone to long-duration in-kernel looping. This commit currently instruments only RCU-tasks. Future possibilities include also instrumenting RCU, RCU-bh, and RCU-sched in order to reduce IPI usage. Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Diffstat (limited to 'include/linux/rcupdate.h')
-rw-r--r--include/linux/rcupdate.h13
1 files changed, 13 insertions, 0 deletions
diff --git a/include/linux/rcupdate.h b/include/linux/rcupdate.h
index 3432063f4c87..473350462d04 100644
--- a/include/linux/rcupdate.h
+++ b/include/linux/rcupdate.h
@@ -330,6 +330,19 @@ static inline void rcu_user_hooks_switch(struct task_struct *prev,
#define rcu_note_voluntary_context_switch(t) do { } while (0)
#endif /* #else #ifdef CONFIG_TASKS_RCU */
+/**
+ * cond_resched_rcu_qs - Report potential quiescent states to RCU
+ *
+ * This macro resembles cond_resched(), except that it is defined to
+ * report potential quiescent states to RCU-tasks even if the cond_resched()
+ * machinery were to be shut off, as some advocate for PREEMPT kernels.
+ */
+#define cond_resched_rcu_qs() \
+do { \
+ rcu_note_voluntary_context_switch(current); \
+ cond_resched(); \
+} while (0)
+
#if defined(CONFIG_DEBUG_LOCK_ALLOC) || defined(CONFIG_RCU_TRACE) || defined(CONFIG_SMP)
bool __rcu_is_watching(void);
#endif /* #if defined(CONFIG_DEBUG_LOCK_ALLOC) || defined(CONFIG_RCU_TRACE) || defined(CONFIG_SMP) */