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authorPaul E. McKenney <paulmck@linux.vnet.ibm.com>2014-03-14 16:37:08 -0700
committerPaul E. McKenney <paulmck@linux.vnet.ibm.com>2014-03-20 17:12:25 -0700
commit765a3f4fed708ae429ee095914a7897acb3a65bd (patch)
tree1a33b4e0e88cdebf60855f6c3b102819ed6986b0 /include/linux
parentf5604f67fe8cbd6f2088b20b9463f721aa613d4b (diff)
rcu: Provide grace-period piggybacking API
The following pattern is currently not well supported by RCU: 1. Make data element inaccessible to RCU readers. 2. Do work that probably lasts for more than one grace period. 3. Do something to make sure RCU readers in flight before #1 above have completed. Here are some things that could currently be done: a. Do a synchronize_rcu() unconditionally at either #1 or #3 above. This works, but imposes needless work and latency. b. Post an RCU callback at #1 above that does a wakeup, then wait for the wakeup at #3. This works well, but likely results in an extra unneeded grace period. Open-coding this is also a bit more semi-tricky code than would be good. This commit therefore adds get_state_synchronize_rcu() and cond_synchronize_rcu() APIs. Call get_state_synchronize_rcu() at #1 above and pass its return value to cond_synchronize_rcu() at #3 above. This results in a call to synchronize_rcu() if no grace period has elapsed between #1 and #3, but requires only a load, comparison, and memory barrier if a full grace period did elapse. Requested-by: Peter Zijlstra <peterz@infradead.org> Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com> Acked-by: Peter Zijlstra <peterz@infradead.org>
Diffstat (limited to 'include/linux')
-rw-r--r--include/linux/rcutiny.h10
-rw-r--r--include/linux/rcutree.h2
2 files changed, 12 insertions, 0 deletions
diff --git a/include/linux/rcutiny.h b/include/linux/rcutiny.h
index e8cb6e3b52a7..425c659d54e5 100644
--- a/include/linux/rcutiny.h
+++ b/include/linux/rcutiny.h
@@ -27,6 +27,16 @@
#include <linux/cache.h>
+static inline unsigned long get_state_synchronize_rcu(void)
+{
+ return 0;
+}
+
+static inline void cond_synchronize_rcu(unsigned long oldstate)
+{
+ might_sleep();
+}
+
static inline void rcu_barrier_bh(void)
{
wait_rcu_gp(call_rcu_bh);
diff --git a/include/linux/rcutree.h b/include/linux/rcutree.h
index e9c63884df0a..a59ca05fd4e3 100644
--- a/include/linux/rcutree.h
+++ b/include/linux/rcutree.h
@@ -76,6 +76,8 @@ static inline void synchronize_rcu_bh_expedited(void)
void rcu_barrier(void);
void rcu_barrier_bh(void);
void rcu_barrier_sched(void);
+unsigned long get_state_synchronize_rcu(void);
+void cond_synchronize_rcu(unsigned long oldstate);
extern unsigned long rcutorture_testseq;
extern unsigned long rcutorture_vernum;