linux-kernel - [PATCH 04/12] rwsem: consistently use adjustment variable

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Message-Id: <1273634462-2672-5-git-send-email-walken@google.com>
Date:	Tue, 11 May 2010 20:20:54 -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 04/12] rwsem: consistently use adjustment variable

Cleanup: previous change introduced an adjustment variable used in
waking writers; the code to wake readers can be made nicer by making
use of that same variable.

Reducing variable count should hopefully help both humans and compilers
looking at this function :)

Signed-off-by: Michel Lespinasse <walken@...gle.com>
---
 lib/rwsem.c |   15 +++++++--------
 1 files changed, 7 insertions(+), 8 deletions(-)

diff --git a/lib/rwsem.c b/lib/rwsem.c
index 0fb6e38..92c8f8e 100644
--- a/lib/rwsem.c
+++ b/lib/rwsem.c
@@ -52,7 +52,7 @@ __rwsem_do_wake(struct rw_semaphore *sem, int downgrading)
 	struct rwsem_waiter *waiter;
 	struct task_struct *tsk;
 	struct list_head *next;
-	signed long oldcount, woken, loop, adjustment;
+	signed long oldcount, loop, adjustment;
 
 	waiter = list_entry(sem->wait_list.next, struct rwsem_waiter, list);
 	if (!(waiter->flags & RWSEM_WAITING_FOR_WRITE))
@@ -96,9 +96,9 @@ __rwsem_do_wake(struct rw_semaphore *sem, int downgrading)
 	 *   readers before waking any processes up
 	 */
  readers_only:
-	woken = 0;
+	loop = 0;
 	do {
-		woken++;
+		loop++;
 
 		if (waiter->list.next == &sem->wait_list)
 			break;
@@ -108,14 +108,13 @@ __rwsem_do_wake(struct rw_semaphore *sem, int downgrading)
 
 	} while (waiter->flags & RWSEM_WAITING_FOR_READ);
 
-	loop = woken;
-	woken *= RWSEM_ACTIVE_READ_BIAS;
+	adjustment = loop * RWSEM_ACTIVE_READ_BIAS;
 	if (waiter->flags & RWSEM_WAITING_FOR_READ)
 		/* hit end of list above */
-		woken -= RWSEM_WAITING_BIAS;
+		adjustment -= RWSEM_WAITING_BIAS;
 
  retry_readers:
-	oldcount = rwsem_atomic_update(woken, sem) - woken;
+	oldcount = rwsem_atomic_update(adjustment, sem) - adjustment;
 	if (!downgrading && (oldcount & RWSEM_ACTIVE_MASK))
 		/* Someone grabbed the sem already */
 		goto undo_readers;
@@ -144,7 +143,7 @@ __rwsem_do_wake(struct rw_semaphore *sem, int downgrading)
 	goto retry_writer;
 
  undo_readers:
-	if (rwsem_atomic_update(-woken, sem) & RWSEM_ACTIVE_MASK)
+	if (rwsem_atomic_update(-adjustment, sem) & RWSEM_ACTIVE_MASK)
 		goto out;
 	goto retry_readers;
 }
-- 
1.7.0.1

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