From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753575AbbAZHgm (ORCPT ); Mon, 26 Jan 2015 02:36:42 -0500 Received: from smtp2.provo.novell.com ([137.65.250.81]:52174 "EHLO smtp2.provo.novell.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753444AbbAZHgl (ORCPT ); Mon, 26 Jan 2015 02:36:41 -0500 From: Davidlohr Bueso To: Peter Zijlstra , Ingo Molnar Cc: "Paul E. McKenney" , Jason Low , Michel Lespinasse , Tim Chen , linux-kernel@vger.kernel.org, Davidlohr Bueso Subject: [PATCH -tip 0/6] rwsem: Fine tuning Date: Sun, 25 Jan 2015 23:36:03 -0800 Message-Id: <1422257769-14083-1-git-send-email-dave@stgolabs.net> X-Mailer: git-send-email 2.1.2 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hello, First two patches are self descriptive obvious add-ons. The rest are performance enhancements for write-mostly workloads. While this is not our priority (use mutexes instead!!), there are cases where heavy use of writers can severly hurt rwsem performance. For instace, we got reports[1] of writer only issues when converting the i_mmap_rwsem from mutex, on a workload that pathologically pounds on this lock for vma operations: - 81.20% execl [kernel.kallsyms] [k] osq_lock - 100.00% mutex_optimistic_spin __mutex_lock_slowpath - mutex_lock + 47.71% unlink_file_vma + 34.91% vma_adjust + 17.38% vma_link This is enough to make small differences painfully evident. These changes (particularly patch 6/6) recover most (~75%) of the performance regression. Patches 4 and 6 deal with optimistic spinning fine tunning, while patch 5 is an attempt to get tid of two barriers when blocking. While I believe this is safe, it certainly needs more eyeballs, I could have easily overlooked something. Most of these changes are straighforward, but have various implications. Passes multiple x86-64 tests. Thanks! [1] https://lkml.org/lkml/2015/1/7/884 Davidlohr Bueso (6): locking/rwsem: Use task->state helpers locking/rwsem: Document barrier need when waking tasks locking/rwsem: Set lock ownership ASAP locking/rwsem: Avoid deceiving lock spinners locking/rwsem: Optimize slowpath/sleeping locking/rwsem: Check for active lock before bailing on spinning kernel/locking/mutex.c | 2 +- kernel/locking/rwsem-spinlock.c | 7 +++- kernel/locking/rwsem-xadd.c | 71 +++++++++++++++++++++++++++++------------ kernel/locking/rwsem.c | 22 +------------ kernel/locking/rwsem.h | 20 ++++++++++++ 5 files changed, 78 insertions(+), 44 deletions(-) create mode 100644 kernel/locking/rwsem.h -- 2.1.2