From: Michel Lespinasse <walken@google.com>
To: Linus Torvalds <torvalds@linux-foundation.org>,
David Howells <dhowells@redhat.com>, Ingo Molnar <mingo@elte.hu>,
Thomas Gleixner <tglx@linutronix.de>
Cc: LKML <linux-kernel@vger.kernel.org>,
Andrew Morton <akpm@linux-foundation.org>,
Mike Waychison <mikew@google.com>,
Suleiman Souhlal <suleiman@google.com>,
Ying Han <yinghan@google.com>,
Michel Lespinasse <walken@google.com>
Subject: [PATCH 04/12] rwsem: consistently use adjustment variable
Date: Tue, 11 May 2010 20:20:54 -0700 [thread overview]
Message-ID: <1273634462-2672-5-git-send-email-walken@google.com> (raw)
In-Reply-To: <1273634462-2672-1-git-send-email-walken@google.com>
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@google.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
next prev parent reply other threads:[~2010-05-12 3:24 UTC|newest]
Thread overview: 33+ messages / expand[flat|nested] mbox.gz Atom feed top
2010-05-12 3:20 [PATCH 00/12] rwsem changes + down_read_unfair() proposal Michel Lespinasse
2010-05-12 3:20 ` [PATCH 01/12] rwsem: test for no active locks in __rwsem_do_wake undo code Michel Lespinasse
2010-05-12 3:20 ` [PATCH 02/12] rwsem: use single atomic update for sem count when waking up readers Michel Lespinasse
2010-05-12 3:20 ` [PATCH 03/12] rwsem: let RWSEM_WAITING_BIAS represent any number of waiting threads Michel Lespinasse
2010-05-12 3:20 ` Michel Lespinasse [this message]
2010-05-12 3:20 ` [PATCH 05/12] x86 rwsem: take advantage of new RWSEM_WAITING_BIAS semantics Michel Lespinasse
2010-05-12 3:20 ` [PATCH 06/12] rwsem: wake queued readers when other readers are active Michel Lespinasse
2010-05-12 3:20 ` [PATCH 07/12] rwsem: wake queued readers when writer blocks on active read lock Michel Lespinasse
2010-05-12 3:20 ` [PATCH 08/12] rwsem: smaller wrappers around rwsem_down_failed_common Michel Lespinasse
2010-05-12 3:20 ` [PATCH 09/12] generic rwsem: implement down_read_unfair Michel Lespinasse
2010-05-12 3:21 ` [PATCH 10/12] rwsem: down_read_unfair infrastructure support Michel Lespinasse
2010-05-12 3:21 ` [PATCH 11/12] x86 rwsem: down_read_unfair implementation Michel Lespinasse
2010-05-12 3:21 ` [PATCH 12/12] Use down_read_unfair() for /sys/<pid>/exe and /sys/<pid>/maps files Michel Lespinasse
2010-05-12 22:53 ` KOSAKI Motohiro
2010-05-12 23:35 ` Michel Lespinasse
2010-05-13 0:32 ` KOSAKI Motohiro
2010-05-12 10:39 ` [PATCH 01/12] rwsem: test for no active locks in __rwsem_do_wake undo code David Howells
2010-05-12 11:01 ` [PATCH 02/12] rwsem: use single atomic update for sem count when waking up readers David Howells
2010-05-13 0:54 ` Michel Lespinasse
2010-05-12 11:36 ` David Howells
2010-05-12 11:45 ` [PATCH 04/12] rwsem: consistently use adjustment variable David Howells
2010-05-13 1:12 ` Michel Lespinasse
2010-05-12 12:10 ` [PATCH 05/12] x86 rwsem: take advantage of new RWSEM_WAITING_BIAS semantics David Howells
2010-05-12 12:22 ` [PATCH 06/12] rwsem: wake queued readers when other readers are active David Howells
2010-05-13 2:39 ` Michel Lespinasse
2010-05-13 5:41 ` Michel Lespinasse
2010-05-12 12:33 ` [PATCH 07/12] rwsem: wake queued readers when writer blocks on active read lock David Howells
2010-05-12 12:36 ` [PATCH 08/12] rwsem: smaller wrappers around rwsem_down_failed_common David Howells
2010-05-12 12:42 ` David Howells
2010-05-13 2:54 ` Michel Lespinasse
2010-05-12 12:46 ` [PATCH 09/12] generic rwsem: implement down_read_unfair David Howells
2010-05-12 13:08 ` [PATCH 11/12] x86 rwsem: down_read_unfair implementation David Howells
2010-05-12 13:10 ` [PATCH 12/12] Use down_read_unfair() for /sys/<pid>/exe and /sys/<pid>/maps files David Howells
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