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authorLance Roy <ldr709@gmail.com>2017-01-24 00:35:18 +0300
committerPaul E. McKenney <paulmck@linux.vnet.ibm.com>2017-01-25 23:53:20 +0300
commitf2c4689640e9a34bc45c013032185ed4ce47e7ff (patch)
treeb83abdbccba941253a9296379e00d09ce355ec2d /include/linux/srcu.h
parent52d7e48b86fc108e45a656d8e53e4237993c481d (diff)
downloadlinux-f2c4689640e9a34bc45c013032185ed4ce47e7ff.tar.xz
srcu: Implement more-efficient reader counts
SRCU uses two per-cpu counters: a nesting counter to count the number of active critical sections, and a sequence counter to ensure that the nesting counters don't change while they are being added together in srcu_readers_active_idx_check(). This patch instead uses per-cpu lock and unlock counters. Because both counters only increase and srcu_readers_active_idx_check() reads the unlock counter before the lock counter, this achieves the same end without having to increment two different counters in srcu_read_lock(). This also saves a smp_mb() in srcu_readers_active_idx_check(). Possible bug: There is no guarantee that the lock counter won't overflow during srcu_readers_active_idx_check(), as there are no memory barriers around srcu_flip() (see comment in srcu_readers_active_idx_check() for details). However, this problem was already present before this patch. Suggested-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com> Signed-off-by: Lance Roy <ldr709@gmail.com> Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com> Cc: Lai Jiangshan <jiangshanlai@gmail.com> Cc: Peter Zijlstra <peterz@infradead.org> Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Diffstat (limited to 'include/linux/srcu.h')
-rw-r--r--include/linux/srcu.h10
1 files changed, 5 insertions, 5 deletions
diff --git a/include/linux/srcu.h b/include/linux/srcu.h
index dc8eb63c6568..a598cf3ac70c 100644
--- a/include/linux/srcu.h
+++ b/include/linux/srcu.h
@@ -33,9 +33,9 @@
#include <linux/rcupdate.h>
#include <linux/workqueue.h>
-struct srcu_struct_array {
- unsigned long c[2];
- unsigned long seq[2];
+struct srcu_array {
+ unsigned long lock_count[2];
+ unsigned long unlock_count[2];
};
struct rcu_batch {
@@ -46,7 +46,7 @@ struct rcu_batch {
struct srcu_struct {
unsigned long completed;
- struct srcu_struct_array __percpu *per_cpu_ref;
+ struct srcu_array __percpu *per_cpu_ref;
spinlock_t queue_lock; /* protect ->batch_queue, ->running */
bool running;
/* callbacks just queued */
@@ -118,7 +118,7 @@ void process_srcu(struct work_struct *work);
* See include/linux/percpu-defs.h for the rules on per-CPU variables.
*/
#define __DEFINE_SRCU(name, is_static) \
- static DEFINE_PER_CPU(struct srcu_struct_array, name##_srcu_array);\
+ static DEFINE_PER_CPU(struct srcu_array, name##_srcu_array);\
is_static struct srcu_struct name = __SRCU_STRUCT_INIT(name)
#define DEFINE_SRCU(name) __DEFINE_SRCU(name, /* not static */)
#define DEFINE_STATIC_SRCU(name) __DEFINE_SRCU(name, static)