From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932111Ab3CKVXb (ORCPT ); Mon, 11 Mar 2013 17:23:31 -0400 Received: from mailout01.c08.mtsvc.net ([205.186.168.189]:33512 "EHLO mailout01.c08.mtsvc.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754949Ab3CKVPe (ORCPT ); Mon, 11 Mar 2013 17:15:34 -0400 From: Peter Hurley To: Greg Kroah-Hartman , Jiri Slaby Cc: Sasha Levin , Dave Jones , Sebastian Andrzej Siewior , Shawn Guo , linux-kernel@vger.kernel.org, linux-serial@vger.kernel.org, Peter Hurley , Michel Lespinasse Subject: [PATCH v5 41/44] tty: Implement ldsem fast path write lock stealing Date: Mon, 11 Mar 2013 16:45:01 -0400 Message-Id: <1363034704-28036-42-git-send-email-peter@hurleysoftware.com> X-Mailer: git-send-email 1.8.1.2 In-Reply-To: <1363034704-28036-1-git-send-email-peter@hurleysoftware.com> References: <1361390599-15195-1-git-send-email-peter@hurleysoftware.com> <1363034704-28036-1-git-send-email-peter@hurleysoftware.com> X-Authenticated-User: 125194 peter@hurleysoftware.com Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Even with waiting writers, if the lock can be grabbed by a new writer, simply grab it. Derived from Michel Lespinasse's write lock stealing work on rwsem. Cc: Michel Lespinasse Signed-off-by: Peter Hurley --- drivers/tty/tty_ldsem.c | 18 +++++++++++------- 1 file changed, 11 insertions(+), 7 deletions(-) diff --git a/drivers/tty/tty_ldsem.c b/drivers/tty/tty_ldsem.c index 372e897..fd95950 100644 --- a/drivers/tty/tty_ldsem.c +++ b/drivers/tty/tty_ldsem.c @@ -325,7 +325,7 @@ static inline int __ldsem_down_write_nested(struct ld_semaphore *sem, count = atomic_long_add_return(LDSEM_WRITE_BIAS, (atomic_long_t *)&sem->count); - if (count != LDSEM_WRITE_BIAS) { + if ((count & LDSEM_ACTIVE_MASK) != LDSEM_ACTIVE_BIAS) { lock_stat(sem, contended); if (!down_write_failed(sem, timeout)) { lockdep_release(sem, 1, _RET_IP_); @@ -380,12 +380,16 @@ int ldsem_down_write_trylock(struct ld_semaphore *sem) { long count; - count = atomic_long_cmpxchg(&sem->count, LDSEM_UNLOCKED, - LDSEM_WRITE_BIAS); - if (count == LDSEM_UNLOCKED) { - lockdep_acquire(sem, 0, 1, _RET_IP_); - lock_stat(sem, acquired); - return 1; + while (((count = sem->count) & LDSEM_ACTIVE_MASK) == 0) { + long tmp; + + tmp = atomic_long_cmpxchg(&sem->count, count, + count + LDSEM_WRITE_BIAS); + if (count == tmp) { + lockdep_acquire(sem, 0, 1, _RET_IP_); + lock_stat(sem, acquired); + return 1; + } } return 0; } -- 1.8.1.2