From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from dkim2.fusionio.com ([66.114.96.54]:45514 "EHLO dkim2.fusionio.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751562Ab3ISPsL (ORCPT ); Thu, 19 Sep 2013 11:48:11 -0400 Received: from mx2.fusionio.com (unknown [10.101.1.160]) by dkim2.fusionio.com (Postfix) with ESMTP id EA8389A0404 for ; Thu, 19 Sep 2013 09:48:10 -0600 (MDT) From: Josef Bacik To: CC: , , , , Subject: [PATCH 1/2] rwsem: add rwsem_is_contended V2 Date: Thu, 19 Sep 2013 11:48:07 -0400 Message-ID: <1379605688-987-1-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 --- 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 | 13 +++++++++++++ 1 file changed, 13 insertions(+) diff --git a/include/linux/rwsem.h b/include/linux/rwsem.h index 0616ffe..c340493 100644 --- a/include/linux/rwsem.h +++ b/include/linux/rwsem.h @@ -75,6 +75,19 @@ 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 the opposite type is wanting access to the + * lock. + */ +static inline int rwsem_is_contended(struct rw_semaphore *sem) +{ + if (!list_empty(&sem->wait_list)) + return 1; + return 0; +} + +/* * lock for reading */ extern void down_read(struct rw_semaphore *sem); -- 1.8.3.1