Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752828Ab3ISPsN (ORCPT ); Thu, 19 Sep 2013 11:48:13 -0400 Received: from dkim2.fusionio.com ([66.114.96.54]:45513 "EHLO dkim2.fusionio.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751157Ab3ISPsL (ORCPT ); Thu, 19 Sep 2013 11:48:11 -0400 X-ASG-Debug-ID: 1379605690-0421b50220406c50001-xx1T2L X-Barracuda-Envelope-From: JBacik@fusionio.com From: Josef Bacik To: CC: , , , , Subject: [PATCH 1/2] rwsem: add rwsem_is_contended V2 Date: Thu, 19 Sep 2013 11:48:07 -0400 X-ASG-Orig-Subj: [PATCH 1/2] rwsem: add rwsem_is_contended V2 Message-ID: <1379605688-987-1-git-send-email-jbacik@fusionio.com> X-Mailer: git-send-email 1.8.3.1 MIME-Version: 1.0 Content-Type: text/plain X-Originating-IP: [10.101.1.160] X-Barracuda-Connect: cas1.int.fusionio.com[10.101.1.40] X-Barracuda-Start-Time: 1379605690 X-Barracuda-Encrypted: AES128-SHA X-Barracuda-URL: http://10.101.1.181:8000/cgi-mod/mark.cgi X-Barracuda-Spam-Score: 0.00 X-Barracuda-Spam-Status: No, SCORE=0.00 using global scores of TAG_LEVEL=1000.0 QUARANTINE_LEVEL=1000.0 KILL_LEVEL=9.0 tests=BSF_SC0_MISMATCH_TO X-Barracuda-Spam-Report: Code version 3.2, rules version 3.2.2.140754 Rule breakdown below pts rule name description ---- ---------------------- -------------------------------------------------- 0.00 BSF_SC0_MISMATCH_TO Envelope rcpt doesn't match header Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1546 Lines: 46 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 -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/