Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1758202AbcCVRrF (ORCPT ); Tue, 22 Mar 2016 13:47:05 -0400 Received: from g1t6214.austin.hp.com ([15.73.96.122]:42583 "EHLO g1t6214.austin.hp.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1756021AbcCVRrD (ORCPT ); Tue, 22 Mar 2016 13:47:03 -0400 From: Waiman Long To: Ingo Molnar Cc: Peter Zijlstra , linux-kernel@vger.kernel.org, Linus Torvalds , Ding Tianhong , Jason Low , Davidlohr Bueso , "Paul E. McKenney" , Thomas Gleixner , Will Deacon , Tim Chen , Waiman Long Subject: [PATCH v3 0/3] locking/mutex: Enable optimistic spinning of lock waiter Date: Tue, 22 Mar 2016 13:46:41 -0400 Message-Id: <1458668804-10138-1-git-send-email-Waiman.Long@hpe.com> X-Mailer: git-send-email 1.7.1 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2393 Lines: 56 v2->v3: - Remove patch 4 as it is not useful. - Allow need_resched() check for waiter & add more comments about changes to address issues raised by PeterZ. v1->v2: - Set task state to running before doing optimistic spinning. - Add 2 more patches to handle possible missed wakeups and wasteful spinning in try_to_wake_up() function. This patchset is a variant of PeterZ's "locking/mutex: Avoid spinner vs waiter starvation" patch. The major difference is that the waiter-spinner won't enter into the OSQ used by the spinners. Instead, it will spin directly on the lock in parallel with the queue head of the OSQ. So there will be a bit more cacheline contention on the lock cacheline, but that shouldn't cause noticeable impact on system performance. This patchset tries to address 2 issues with Peter's patch: 1) Ding Tianhong still find that hanging task could happen in some cases. 2) Jason Low found that there was performance regression for some AIM7 workloads. By making the waiter-spinner to spin directly on the mutex, it will increase the chance for the waiter-spinner to get the lock instead of waiting in the OSQ for its turn. Patch 1 modifies the mutex_optimistic_spin() function to enable it to be called by a waiter-spinner that doesn't need to go into the OSQ. Patch 2 modifies the mutex locking slowpath to make the waiter call mutex_optimistic_spin() to do spinning after being waken up. Patch 3 reverses the sequence of setting task state and changing mutex count to -1 to prevent the possibility of missed wakeup. Patch 4 modifies the wakeup code to abandon the wakeup operation while spinning on the on_cpu flag if the task has changed back to a non-sleeping state. My own test on a 4-socket E7-4820 v3 system showed a regression of about 4% in the high_systime workload with Peter's patch which this new patch effectively eliminates. Testing on an 8-socket Westmere-EX server, however, has performance change from -9% to than +140% on the fserver workload of AIM7 depending on how the system was set up. Waiman Long (3): locking/mutex: Add waiter parameter to mutex_optimistic_spin() locking/mutex: Enable optimistic spinning of woken task in wait queue locking/mutex: Avoid missed wakeup of mutex waiter kernel/locking/mutex.c | 126 ++++++++++++++++++++++++++++++++++-------------- 1 files changed, 90 insertions(+), 36 deletions(-)