rcu: add a helper to report consolidated flavor QS

[sfrench/cifs-2.6.git] / include / linux / rcupdate.h

diff --git a/include/linux/rcupdate.h b/include/linux/rcupdate.h
index 16f519914415ebf5592e75be67e8660339d6b0e7..17d7ed5f3ae6e5c612acd4261be763855069946d 100644 (file)
--- a/include/linux/rcupdate.h
+++ b/include/linux/rcupdate.h
@@ -247,6 +247,37 @@ do { \
        cond_resched(); \
 } while (0)
 
+/**
+ * rcu_softirq_qs_periodic - Report RCU and RCU-Tasks quiescent states
+ * @old_ts: jiffies at start of processing.
+ *
+ * This helper is for long-running softirq handlers, such as NAPI threads in
+ * networking. The caller should initialize the variable passed in as @old_ts
+ * at the beginning of the softirq handler. When invoked frequently, this macro
+ * will invoke rcu_softirq_qs() every 100 milliseconds thereafter, which will
+ * provide both RCU and RCU-Tasks quiescent states. Note that this macro
+ * modifies its old_ts argument.
+ *
+ * Because regions of code that have disabled softirq act as RCU read-side
+ * critical sections, this macro should be invoked with softirq (and
+ * preemption) enabled.
+ *
+ * The macro is not needed when CONFIG_PREEMPT_RT is defined. RT kernels would
+ * have more chance to invoke schedule() calls and provide necessary quiescent
+ * states. As a contrast, calling cond_resched() only won't achieve the same
+ * effect because cond_resched() does not provide RCU-Tasks quiescent states.
+ */
+#define rcu_softirq_qs_periodic(old_ts) \
+do { \
+       if (!IS_ENABLED(CONFIG_PREEMPT_RT) && \
+           time_after(jiffies, (old_ts) + HZ / 10)) { \
+               preempt_disable(); \
+               rcu_softirq_qs(); \
+               preempt_enable(); \
+               (old_ts) = jiffies; \
+       } \
+} while (0)
+
 /*
  * Infrastructure to implement the synchronize_() primitives in
  * TREE_RCU and rcu_barrier_() primitives in TINY_RCU.