summaryrefslogtreecommitdiff
path: root/include/linux/percpu-rwsem.h
diff options
context:
space:
mode:
authorDavidlohr Bueso <dave@stgolabs.net>2017-01-11 18:22:26 +0300
committerIngo Molnar <mingo@kernel.org>2017-01-14 13:14:35 +0300
commit52b94129f274937e4c25dd17b76697664a3c43c9 (patch)
treeefcc4d7a0159e0bf33961532430e15b0ec66fcdb /include/linux/percpu-rwsem.h
parent8f95c90ceb541a38ac16fec48c05142ef1450c25 (diff)
downloadlinux-52b94129f274937e4c25dd17b76697664a3c43c9.tar.xz
locking/percpu-rwsem: Replace waitqueue with rcuwait
The use of any kind of wait queue is an overkill for pcpu-rwsems. While one option would be to use the less heavy simple (swait) flavor, this is still too much for what pcpu-rwsems needs. For one, we do not care about any sort of queuing in that the only (rare) time writers (and readers, for that matter) are queued is when trying to acquire the regular contended rw_sem. There cannot be any further queuing as writers are serialized by the rw_sem in the first place. Given that percpu_down_write() must not be called after exit_notify(), we can replace the bulky waitqueue with rcuwait such that a writer can wait for its turn to take the lock. As such, we can avoid the queue handling and locking overhead. Signed-off-by: Davidlohr Bueso <dbueso@suse.de> Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org> Reviewed-by: Oleg Nesterov <oleg@redhat.com> Cc: Andrew Morton <akpm@linux-foundation.org> Cc: Linus Torvalds <torvalds@linux-foundation.org> Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Thomas Gleixner <tglx@linutronix.de> Cc: dave@stgolabs.net Link: http://lkml.kernel.org/r/1484148146-14210-3-git-send-email-dave@stgolabs.net Signed-off-by: Ingo Molnar <mingo@kernel.org>
Diffstat (limited to 'include/linux/percpu-rwsem.h')
-rw-r--r--include/linux/percpu-rwsem.h8
1 files changed, 4 insertions, 4 deletions
diff --git a/include/linux/percpu-rwsem.h b/include/linux/percpu-rwsem.h
index 5b2e6159b744..93664f022ecf 100644
--- a/include/linux/percpu-rwsem.h
+++ b/include/linux/percpu-rwsem.h
@@ -4,15 +4,15 @@
#include <linux/atomic.h>
#include <linux/rwsem.h>
#include <linux/percpu.h>
-#include <linux/wait.h>
+#include <linux/rcuwait.h>
#include <linux/rcu_sync.h>
#include <linux/lockdep.h>
struct percpu_rw_semaphore {
struct rcu_sync rss;
unsigned int __percpu *read_count;
- struct rw_semaphore rw_sem;
- wait_queue_head_t writer;
+ struct rw_semaphore rw_sem; /* slowpath */
+ struct rcuwait writer; /* blocked writer */
int readers_block;
};
@@ -22,7 +22,7 @@ static struct percpu_rw_semaphore name = { \
.rss = __RCU_SYNC_INITIALIZER(name.rss, RCU_SCHED_SYNC), \
.read_count = &__percpu_rwsem_rc_##name, \
.rw_sem = __RWSEM_INITIALIZER(name.rw_sem), \
- .writer = __WAIT_QUEUE_HEAD_INITIALIZER(name.writer), \
+ .writer = __RCUWAIT_INITIALIZER(name.writer), \
}
extern int __percpu_down_read(struct percpu_rw_semaphore *, int);