From patchwork Wed Oct 29 20:19:04 2014 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Waiman Long X-Patchwork-Id: 5191441 Return-Path: X-Original-To: patchwork-kvm@patchwork.kernel.org Delivered-To: patchwork-parsemail@patchwork2.web.kernel.org Received: from mail.kernel.org (mail.kernel.org [198.145.19.201]) by patchwork2.web.kernel.org (Postfix) with ESMTP id 1756CC11AC for ; Wed, 29 Oct 2014 20:22:54 +0000 (UTC) Received: from mail.kernel.org (localhost [127.0.0.1]) by mail.kernel.org (Postfix) with ESMTP id 2122820172 for ; Wed, 29 Oct 2014 20:22:53 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 1A06020149 for ; Wed, 29 Oct 2014 20:22:52 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1757170AbaJ2UTn (ORCPT ); Wed, 29 Oct 2014 16:19:43 -0400 Received: from g4t3426.houston.hp.com ([15.201.208.54]:20845 "EHLO g4t3426.houston.hp.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1757107AbaJ2UTm (ORCPT ); Wed, 29 Oct 2014 16:19:42 -0400 Received: from g4t3433.houston.hp.com (g4t3433.houston.hp.com [16.210.25.219]) by g4t3426.houston.hp.com (Postfix) with ESMTP id 9AF2663; Wed, 29 Oct 2014 20:19:41 +0000 (UTC) Received: from RHEL65.localdomain (ospra0.fc.hp.com [16.79.38.117]) by g4t3433.houston.hp.com (Postfix) with ESMTP id B2A6D68; Wed, 29 Oct 2014 20:19:37 +0000 (UTC) From: Waiman Long To: Thomas Gleixner , Ingo Molnar , "H. Peter Anvin" , Peter Zijlstra Cc: linux-arch@vger.kernel.org, x86@kernel.org, linux-kernel@vger.kernel.org, virtualization@lists.linux-foundation.org, xen-devel@lists.xenproject.org, kvm@vger.kernel.org, Paolo Bonzini , Konrad Rzeszutek Wilk , Boris Ostrovsky , "Paul E. McKenney" , Rik van Riel , Linus Torvalds , Raghavendra K T , David Vrabel , Oleg Nesterov , Scott J Norton , Douglas Hatch , Waiman Long , Peter Zijlstra Subject: [PATCH v13 04/11] qspinlock: Extract out code snippets for the next patch Date: Wed, 29 Oct 2014 16:19:04 -0400 Message-Id: <1414613951-32532-5-git-send-email-Waiman.Long@hp.com> X-Mailer: git-send-email 1.7.1 In-Reply-To: <1414613951-32532-1-git-send-email-Waiman.Long@hp.com> References: <1414613951-32532-1-git-send-email-Waiman.Long@hp.com> Sender: kvm-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: kvm@vger.kernel.org X-Spam-Status: No, score=-7.5 required=5.0 tests=BAYES_00, RCVD_IN_DNSWL_HI, RP_MATCHES_RCVD, UNPARSEABLE_RELAY autolearn=unavailable version=3.3.1 X-Spam-Checker-Version: SpamAssassin 3.3.1 (2010-03-16) on mail.kernel.org X-Virus-Scanned: ClamAV using ClamSMTP This is a preparatory patch that extracts out the following 2 code snippets to prepare for the next performance optimization patch. 1) the logic for the exchange of new and previous tail code words into a new xchg_tail() function. 2) the logic for clearing the pending bit and setting the locked bit into a new clear_pending_set_locked() function. This patch also simplifies the trylock operation before queuing by calling queue_spin_trylock() directly. Signed-off-by: Waiman Long Signed-off-by: Peter Zijlstra --- include/asm-generic/qspinlock_types.h | 2 + kernel/locking/qspinlock.c | 91 +++++++++++++++++++++----------- 2 files changed, 62 insertions(+), 31 deletions(-) diff --git a/include/asm-generic/qspinlock_types.h b/include/asm-generic/qspinlock_types.h index 4196694..88d647c 100644 --- a/include/asm-generic/qspinlock_types.h +++ b/include/asm-generic/qspinlock_types.h @@ -58,6 +58,8 @@ typedef struct qspinlock { #define _Q_TAIL_CPU_BITS (32 - _Q_TAIL_CPU_OFFSET) #define _Q_TAIL_CPU_MASK _Q_SET_MASK(TAIL_CPU) +#define _Q_TAIL_MASK (_Q_TAIL_IDX_MASK | _Q_TAIL_CPU_MASK) + #define _Q_LOCKED_VAL (1U << _Q_LOCKED_OFFSET) #define _Q_PENDING_VAL (1U << _Q_PENDING_OFFSET) diff --git a/kernel/locking/qspinlock.c b/kernel/locking/qspinlock.c index 226b11d..48bd2ad 100644 --- a/kernel/locking/qspinlock.c +++ b/kernel/locking/qspinlock.c @@ -95,6 +95,54 @@ static inline struct mcs_spinlock *decode_tail(u32 tail) #define _Q_LOCKED_PENDING_MASK (_Q_LOCKED_MASK | _Q_PENDING_MASK) /** + * clear_pending_set_locked - take ownership and clear the pending bit. + * @lock: Pointer to queue spinlock structure + * @val : Current value of the queue spinlock 32-bit word + * + * *,1,0 -> *,0,1 + */ +static __always_inline void +clear_pending_set_locked(struct qspinlock *lock, u32 val) +{ + u32 new, old; + + for (;;) { + new = (val & ~_Q_PENDING_MASK) | _Q_LOCKED_VAL; + + old = atomic_cmpxchg(&lock->val, val, new); + if (old == val) + break; + + val = old; + } +} + +/** + * xchg_tail - Put in the new queue tail code word & retrieve previous one + * @lock : Pointer to queue spinlock structure + * @tail : The new queue tail code word + * Return: The previous queue tail code word + * + * xchg(lock, tail) + * + * p,*,* -> n,*,* ; prev = xchg(lock, node) + */ +static __always_inline u32 xchg_tail(struct qspinlock *lock, u32 tail) +{ + u32 old, new, val = atomic_read(&lock->val); + + for (;;) { + new = (val & _Q_LOCKED_PENDING_MASK) | tail; + old = atomic_cmpxchg(&lock->val, val, new); + if (old == val) + break; + + val = old; + } + return old; +} + +/** * queue_spin_lock_slowpath - acquire the queue spinlock * @lock: Pointer to queue spinlock structure * @val: Current value of the queue spinlock 32-bit word @@ -176,15 +224,7 @@ void queue_spin_lock_slowpath(struct qspinlock *lock, u32 val) * * *,1,0 -> *,0,1 */ - for (;;) { - new = (val & ~_Q_PENDING_MASK) | _Q_LOCKED_VAL; - - old = atomic_cmpxchg(&lock->val, val, new); - if (old == val) - break; - - val = old; - } + clear_pending_set_locked(lock, val); return; /* @@ -201,37 +241,26 @@ queue: node->next = NULL; /* - * We have already touched the queueing cacheline; don't bother with - * pending stuff. - * - * trylock || xchg(lock, node) - * - * 0,0,0 -> 0,0,1 ; no tail, not locked -> no tail, locked. - * p,y,x -> n,y,x ; tail was p -> tail is n; preserving locked. + * We touched a (possibly) cold cacheline in the per-cpu queue node; + * attempt the trylock once more in the hope someone let go while we + * weren't watching. */ - for (;;) { - new = _Q_LOCKED_VAL; - if (val) - new = tail | (val & _Q_LOCKED_PENDING_MASK); - - old = atomic_cmpxchg(&lock->val, val, new); - if (old == val) - break; - - val = old; - } + if (queue_spin_trylock(lock)) + goto release; /* - * we won the trylock; forget about queueing. + * We have already touched the queueing cacheline; don't bother with + * pending stuff. + * + * p,*,* -> n,*,* */ - if (new == _Q_LOCKED_VAL) - goto release; + old = xchg_tail(lock, tail); /* * if there was a previous node; link it and wait until reaching the * head of the waitqueue. */ - if (old & ~_Q_LOCKED_PENDING_MASK) { + if (old & _Q_TAIL_MASK) { prev = decode_tail(old); ACCESS_ONCE(prev->next) = node;