From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S964971AbaE3Ppb (ORCPT ); Fri, 30 May 2014 11:45:31 -0400 Received: from g4t3426.houston.hp.com ([15.201.208.54]:2793 "EHLO g4t3426.houston.hp.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S964920AbaE3Pp0 (ORCPT ); Fri, 30 May 2014 11:45:26 -0400 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 , Gleb Natapov , Scott J Norton , Chegu Vinod , Waiman Long Subject: [PATCH v11 04/16] qspinlock: Extract out the exchange of tail code word Date: Fri, 30 May 2014 11:43:50 -0400 Message-Id: <1401464642-33890-5-git-send-email-Waiman.Long@hp.com> X-Mailer: git-send-email 1.7.1 In-Reply-To: <1401464642-33890-1-git-send-email-Waiman.Long@hp.com> References: <1401464642-33890-1-git-send-email-Waiman.Long@hp.com> Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org This patch extracts the logic for the exchange of new and previous tail code words into a new xchg_tail() function which can be optimized in a later patch. Signed-off-by: Waiman Long --- include/asm-generic/qspinlock_types.h | 2 + kernel/locking/qspinlock.c | 58 ++++++++++++++++++++------------ 2 files changed, 38 insertions(+), 22 deletions(-) diff --git a/include/asm-generic/qspinlock_types.h b/include/asm-generic/qspinlock_types.h index bd25081..ed5d89a 100644 --- a/include/asm-generic/qspinlock_types.h +++ b/include/asm-generic/qspinlock_types.h @@ -61,6 +61,8 @@ 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 1e93c6a..41594a1 100644 --- a/kernel/locking/qspinlock.c +++ b/kernel/locking/qspinlock.c @@ -86,6 +86,31 @@ static inline struct mcs_spinlock *decode_tail(u32 tail) #define _Q_LOCKED_PENDING_MASK (_Q_LOCKED_MASK | _Q_PENDING_MASK) /** + * 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 @@ -182,36 +207,25 @@ queue: node->next = NULL; /* - * we already touched the queueing cacheline; don't bother with pending - * stuff. - * - * trylock || xchg(lock, node) - * - * 0,0,0 -> 0,0,1 ; trylock - * p,y,x -> n,y,x ; prev = xchg(lock, node) + * 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 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. */ - if (old & ~_Q_LOCKED_PENDING_MASK) { + if (old & _Q_TAIL_MASK) { prev = decode_tail(old); ACCESS_ONCE(prev->next) = node; -- 1.7.1