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Message-Id: <1273840782-5920-9-git-send-email-walken@google.com>
Date: Fri, 14 May 2010 05:39:40 -0700
From: Michel Lespinasse <walken@...gle.com>
To: Linus Torvalds <torvalds@...ux-foundation.org>,
David Howells <dhowells@...hat.com>,
Ingo Molnar <mingo@...e.hu>,
Thomas Gleixner <tglx@...utronix.de>
Cc: LKML <linux-kernel@...r.kernel.org>,
Andrew Morton <akpm@...ux-foundation.org>,
Mike Waychison <mikew@...gle.com>,
Suleiman Souhlal <suleiman@...gle.com>,
Ying Han <yinghan@...gle.com>,
Michel Lespinasse <walken@...gle.com>
Subject: [PATCH 08/10] rwsem: down_read_unfair infrastructure support
Add rwsem_down_read_unfair_failed() function in the non-generic rwsem
library code, similar to rwsem_down_read_failed() except that blocked
threads are placed at the head of the queue.
Signed-off-by: Michel Lespinasse <walken@...gle.com>
---
lib/rwsem.c | 22 +++++++++++++++++++++-
1 files changed, 21 insertions(+), 1 deletions(-)
diff --git a/lib/rwsem.c b/lib/rwsem.c
index 2dd1a1b..f0589b2 100644
--- a/lib/rwsem.c
+++ b/lib/rwsem.c
@@ -34,6 +34,7 @@ struct rwsem_waiter {
unsigned int flags;
#define RWSEM_WAITING_FOR_READ 0x00000001
#define RWSEM_WAITING_FOR_WRITE 0x00000002
+#define RWSEM_UNFAIR 0x00000004
};
/* Wake types for __rwsem_do_wake(). Note that RWSEM_WAKE_NO_ACTIVE and
@@ -186,7 +187,11 @@ rwsem_down_failed_common(struct rw_semaphore *sem,
if (list_empty(&sem->wait_list))
adjustment += RWSEM_WAITING_BIAS;
- list_add_tail(&waiter.list, &sem->wait_list);
+
+ if (flags & RWSEM_UNFAIR)
+ list_add(&waiter.list, &sem->wait_list);
+ else
+ list_add_tail(&waiter.list, &sem->wait_list);
/* we're now waiting on the lock, but no longer actively locking */
count = rwsem_atomic_update(adjustment, sem);
@@ -228,6 +233,21 @@ rwsem_down_read_failed(struct rw_semaphore *sem)
-RWSEM_ACTIVE_READ_BIAS);
}
+#ifdef __HAVE_DOWN_READ_UNFAIR
+
+/*
+ * wait for the read lock to be granted - skip waiting threads
+ */
+asmregparm struct rw_semaphore __sched *
+rwsem_down_read_unfair_failed(struct rw_semaphore *sem)
+{
+ return rwsem_down_failed_common(sem,
+ RWSEM_WAITING_FOR_READ | RWSEM_UNFAIR,
+ -RWSEM_ACTIVE_READ_BIAS);
+}
+
+#endif
+
/*
* wait for the write lock to be granted
*/
--
1.7.0.1
--
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