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authorDavidlohr Bueso <dave@stgolabs.net>2015-01-30 01:14:25 -0800
committerIngo Molnar <mingo@kernel.org>2015-02-18 16:57:13 +0100
commit7a215f89a0335582292ec6f3edaa3abd570da75a (patch)
treee2f21b6e285b864eab87f5a13a1cbf91b2152eb4 /kernel/locking/rwsem-xadd.c
parent49e4b2bcf7b812e985e65b6c8a0255b1520a6e7e (diff)
downloadlinux-7a215f89a0335582292ec6f3edaa3abd570da75a.tar.bz2
locking/rwsem: Set lock ownership ASAP
In order to optimize the spinning step, we need to set the lock owner as soon as the lock is acquired; after a successful counter cmpxchg operation, that is. This is particularly useful as rwsems need to set the owner to nil for readers, so there is a greater chance of falling out of the spinning. Currently we only set the owner much later in the game, in the more generic level -- latency can be specially bad when waiting for a node->next pointer when releasing the osq in up_write calls. As such, update the owner inside rwsem_try_write_lock (when the lock is obtained after blocking) and rwsem_try_write_lock_unqueued (when the lock is obtained while spinning). This requires creating a new internal rwsem.h header to share the owner related calls. Also cleanup some headers for mutex and rwsem. Suggested-by: Peter Zijlstra <peterz@infradead.org> Signed-off-by: Davidlohr Bueso <dbueso@suse.de> Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org> Cc: Jason Low <jason.low2@hp.com> Cc: Linus Torvalds <torvalds@linux-foundation.org> Cc: Michel Lespinasse <walken@google.com> Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com> Cc: Tim Chen <tim.c.chen@linux.intel.com> Link: http://lkml.kernel.org/r/1422609267-15102-4-git-send-email-dave@stgolabs.net Signed-off-by: Ingo Molnar <mingo@kernel.org>
Diffstat (limited to 'kernel/locking/rwsem-xadd.c')
-rw-r--r--kernel/locking/rwsem-xadd.c8
1 files changed, 6 insertions, 2 deletions
diff --git a/kernel/locking/rwsem-xadd.c b/kernel/locking/rwsem-xadd.c
index 82aba467564a..07713e5d9713 100644
--- a/kernel/locking/rwsem-xadd.c
+++ b/kernel/locking/rwsem-xadd.c
@@ -14,8 +14,9 @@
#include <linux/init.h>
#include <linux/export.h>
#include <linux/sched/rt.h>
+#include <linux/osq_lock.h>
-#include "mcs_spinlock.h"
+#include "rwsem.h"
/*
* Guide to the rw_semaphore's count field for common values.
@@ -265,6 +266,7 @@ static inline bool rwsem_try_write_lock(long count, struct rw_semaphore *sem)
RWSEM_ACTIVE_WRITE_BIAS) == RWSEM_WAITING_BIAS) {
if (!list_is_singular(&sem->wait_list))
rwsem_atomic_update(RWSEM_WAITING_BIAS, sem);
+ rwsem_set_owner(sem);
return true;
}
@@ -284,8 +286,10 @@ static inline bool rwsem_try_write_lock_unqueued(struct rw_semaphore *sem)
return false;
old = cmpxchg(&sem->count, count, count + RWSEM_ACTIVE_WRITE_BIAS);
- if (old == count)
+ if (old == count) {
+ rwsem_set_owner(sem);
return true;
+ }
count = old;
}