From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from dkim2.fusionio.com ([66.114.96.54]:49933 "EHLO dkim2.fusionio.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750984Ab3IZN0j (ORCPT ); Thu, 26 Sep 2013 09:26:39 -0400 Received: from mx1.fusionio.com (unknown [10.101.1.160]) by dkim2.fusionio.com (Postfix) with ESMTP id 1581A9A0691 for ; Thu, 26 Sep 2013 07:26:39 -0600 (MDT) From: Josef Bacik To: CC: , , , , Subject: [PATCH 1/2] rwsem: add rwsem_is_contended V3 Date: Thu, 26 Sep 2013 09:26:35 -0400 Message-ID: <1380201996-17445-1-git-send-email-jbacik@fusionio.com> MIME-Version: 1.0 Content-Type: text/plain Sender: linux-btrfs-owner@vger.kernel.org List-ID: Btrfs needs a simple way to know if it needs to let go of it's read lock on a rwsem. Introduce rwsem_is_contended to check to see if there are any waiters on this rwsem currently. This is just a hueristic, it is meant to be light and not 100% accurate and called by somebody already holding on to the rwsem in either read or write. Thanks, Signed-off-by: Josef Bacik --- V2->V3: fixed the comment and simplified the function as per Peter's suggestions. V1->V2: took everybodys suggestions and simplified it to just one function in rwsem.h so it works for both the spinlock case and non-spinlock case. include/linux/rwsem.h | 11 +++++++++++ 1 file changed, 11 insertions(+) diff --git a/include/linux/rwsem.h b/include/linux/rwsem.h index 0616ffe..03f3b05 100644 --- a/include/linux/rwsem.h +++ b/include/linux/rwsem.h @@ -75,6 +75,17 @@ do { \ } while (0) /* + * This is the same regardless of which rwsem implementation that is being used. + * It is just a heuristic meant to be called by somebody alreadying holding the + * rwsem to see if somebody from an incompatible type is wanting access to the + * lock. + */ +static inline int rwsem_is_contended(struct rw_semaphore *sem) +{ + return !list_empty(&sem->wait_list); +} + +/* * lock for reading */ extern void down_read(struct rw_semaphore *sem); -- 1.8.3.1