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authorDavidlohr Bueso <dave@stgolabs.net>2017-01-11 07:22:26 -0800
committerIngo Molnar <mingo@kernel.org>2017-01-14 11:14:35 +0100
commit52b94129f274937e4c25dd17b76697664a3c43c9 (patch)
treeefcc4d7a0159e0bf33961532430e15b0ec66fcdb /kernel/locking
parent8f95c90ceb541a38ac16fec48c05142ef1450c25 (diff)
downloadop-kernel-dev-52b94129f274937e4c25dd17b76697664a3c43c9.zip
op-kernel-dev-52b94129f274937e4c25dd17b76697664a3c43c9.tar.gz
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 'kernel/locking')
-rw-r--r--kernel/locking/percpu-rwsem.c7
1 files changed, 3 insertions, 4 deletions
diff --git a/kernel/locking/percpu-rwsem.c b/kernel/locking/percpu-rwsem.c
index ce18259..883cf1b 100644
--- a/kernel/locking/percpu-rwsem.c
+++ b/kernel/locking/percpu-rwsem.c
@@ -1,7 +1,6 @@
#include <linux/atomic.h>
#include <linux/rwsem.h>
#include <linux/percpu.h>
-#include <linux/wait.h>
#include <linux/lockdep.h>
#include <linux/percpu-rwsem.h>
#include <linux/rcupdate.h>
@@ -18,7 +17,7 @@ int __percpu_init_rwsem(struct percpu_rw_semaphore *sem,
/* ->rw_sem represents the whole percpu_rw_semaphore for lockdep */
rcu_sync_init(&sem->rss, RCU_SCHED_SYNC);
__init_rwsem(&sem->rw_sem, name, rwsem_key);
- init_waitqueue_head(&sem->writer);
+ rcuwait_init(&sem->writer);
sem->readers_block = 0;
return 0;
}
@@ -103,7 +102,7 @@ void __percpu_up_read(struct percpu_rw_semaphore *sem)
__this_cpu_dec(*sem->read_count);
/* Prod writer to recheck readers_active */
- wake_up(&sem->writer);
+ rcuwait_wake_up(&sem->writer);
}
EXPORT_SYMBOL_GPL(__percpu_up_read);
@@ -160,7 +159,7 @@ void percpu_down_write(struct percpu_rw_semaphore *sem)
*/
/* Wait for all now active readers to complete. */
- wait_event(sem->writer, readers_active_check(sem));
+ rcuwait_wait_event(&sem->writer, readers_active_check(sem));
}
EXPORT_SYMBOL_GPL(percpu_down_write);
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