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Date: Tue, 17 Dec 2013 11:23:59 -0800
From: "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
To: Waiman Long <Waiman.Long@...com>
Cc: Thomas Gleixner <tglx@...utronix.de>,
Ingo Molnar <mingo@...hat.com>,
"H. Peter Anvin" <hpa@...or.com>, Arnd Bergmann <arnd@...db.de>,
linux-arch@...r.kernel.org, x86@...nel.org,
linux-kernel@...r.kernel.org,
Peter Zijlstra <peterz@...radead.org>,
Steven Rostedt <rostedt@...dmis.org>,
Andrew Morton <akpm@...ux-foundation.org>,
Michel Lespinasse <walken@...gle.com>,
Andi Kleen <andi@...stfloor.org>,
Rik van Riel <riel@...hat.com>,
Linus Torvalds <torvalds@...ux-foundation.org>,
Raghavendra K T <raghavendra.kt@...ux.vnet.ibm.com>,
George Spelvin <linux@...izon.com>,
Tim Chen <tim.c.chen@...ux.intel.com>,
"Aswin Chandramouleeswaran\"" <aswin@...com>,
Scott J Norton <scott.norton@...com>
Subject: Re: [PATCH v7 3/4] qrwlock: Use the mcs_spinlock helper functions
for MCS queuing
On Fri, Nov 22, 2013 at 02:04:46PM -0500, Waiman Long wrote:
> There is a pending MCS lock patch series that adds generic MCS lock
> helper functions to do MCS-style locking. This patch will enable
> the queue rwlock to use that generic MCS lock/unlock primitives for
> internal queuing. This patch should only be merged after the merging
> of that generic MCS locking patch.
>
> Signed-off-by: Waiman Long <Waiman.Long@...com>
Reviewed-by: Paul E. McKenney <paulmck@...ux.vnet.ibm.com>
> ---
> include/asm-generic/qrwlock.h | 7 +--
> kernel/locking/qrwlock.c | 83 +++-------------------------------------
> 2 files changed, 9 insertions(+), 81 deletions(-)
>
> diff --git a/include/asm-generic/qrwlock.h b/include/asm-generic/qrwlock.h
> index 9d085cb..335473a 100644
> --- a/include/asm-generic/qrwlock.h
> +++ b/include/asm-generic/qrwlock.h
> @@ -37,10 +37,7 @@
> * the writer field. The least significant 8 bits is the writer field
> * whereas the remaining 24 bits is the reader count.
> */
> -struct qrwnode {
> - struct qrwnode *next;
> - bool wait; /* Waiting flag */
> -};
> +struct mcs_spinlock;
>
> typedef struct qrwlock {
> union qrwcnts {
> @@ -55,7 +52,7 @@ typedef struct qrwlock {
> };
> u32 rw; /* Reader/writer number pair */
> } cnts;
> - struct qrwnode *waitq; /* Tail of waiting queue */
> + struct mcs_spinlock *waitq; /* Tail of waiting queue */
> } arch_rwlock_t;
>
> /*
> diff --git a/kernel/locking/qrwlock.c b/kernel/locking/qrwlock.c
> index ea5553d..b3e5c2b 100644
> --- a/kernel/locking/qrwlock.c
> +++ b/kernel/locking/qrwlock.c
> @@ -20,6 +20,7 @@
> #include <linux/cpumask.h>
> #include <linux/percpu.h>
> #include <linux/hardirq.h>
> +#include <linux/mcs_spinlock.h>
> #include <asm-generic/qrwlock.h>
>
> /*
> @@ -55,76 +56,6 @@
> # endif
> #endif
>
> -#ifndef smp_mb__store_release
> -# ifdef CONFIG_X86
> -# define smp_mb__store_release() barrier()
> -# else
> -# define smp_mb__store_release() smp_mb()
> -# endif
> -#endif
> -
> -/**
> - * wait_in_queue - Add to queue and wait until it is at the head
> - * @lock: Pointer to queue rwlock structure
> - * @node: Node pointer to be added to the queue
> - */
> -static __always_inline void
> -wait_in_queue(struct qrwlock *lock, struct qrwnode *node)
> -{
> - struct qrwnode *prev;
> -
> - node->next = NULL;
> - node->wait = true;
> - prev = xchg(&lock->waitq, node);
> - if (prev) {
> - prev->next = node;
> - /*
> - * Wait until the waiting flag is off
> - */
> - while (ACCESS_ONCE(node->wait))
> - arch_mutex_cpu_relax();
> - smp_mb__load_acquire();
> - }
> -}
> -
> -/**
> - * signal_next - Signal the next one in queue to be at the head
> - * @lock: Pointer to queue rwlock structure
> - * @node: Node pointer to the current head of queue
> - */
> -static __always_inline void
> -signal_next(struct qrwlock *lock, struct qrwnode *node)
> -{
> - struct qrwnode *next;
> -
> - /*
> - * Try to notify the next node first without disturbing the cacheline
> - * of the lock. If that fails, check to see if it is the last node
> - * and so should clear the wait queue.
> - */
> - next = ACCESS_ONCE(node->next);
> - if (likely(next))
> - goto notify_next;
> -
> - /*
> - * Clear the wait queue if it is the last node
> - */
> - if ((ACCESS_ONCE(lock->waitq) == node) &&
> - (cmpxchg(&lock->waitq, node, NULL) == node))
> - return;
> - /*
> - * Wait until the next one in queue set up the next field
> - */
> - while (likely(!(next = ACCESS_ONCE(node->next))))
> - arch_mutex_cpu_relax();
> - /*
> - * The next one in queue is now at the head
> - */
> -notify_next:
> - smp_mb__store_release();
> - ACCESS_ONCE(next->wait) = false;
> -}
> -
> /**
> * rspin_until_writer_unlock - inc reader count & spin until writer is gone
> * @lock: Pointer to queue rwlock structure
> @@ -148,7 +79,7 @@ rspin_until_writer_unlock(struct qrwlock *lock, union qrwcnts cnts)
> */
> void queue_read_lock_slowpath(struct qrwlock *lock)
> {
> - struct qrwnode node;
> + struct mcs_spinlock node;
> union qrwcnts cnts;
>
> /*
> @@ -168,7 +99,7 @@ void queue_read_lock_slowpath(struct qrwlock *lock)
> /*
> * Put the reader into the wait queue
> */
> - wait_in_queue(lock, &node);
> + mcs_spin_lock(&lock->waitq, &node);
>
> /*
> * At the head of the wait queue now, wait until the writer state
> @@ -183,7 +114,7 @@ void queue_read_lock_slowpath(struct qrwlock *lock)
> * Need to have a barrier with read-acquire semantics
> */
> smp_mb__load_acquire();
> - signal_next(lock, &node);
> + mcs_spin_unlock(&lock->waitq, &node);
> }
> EXPORT_SYMBOL(queue_read_lock_slowpath);
>
> @@ -247,12 +178,12 @@ static noinline int queue_write_3step_lock(struct qrwlock *lock)
> */
> void queue_write_lock_slowpath(struct qrwlock *lock)
> {
> - struct qrwnode node;
> + struct mcs_spinlock node;
>
> /*
> * Put the writer into the wait queue
> */
> - wait_in_queue(lock, &node);
> + mcs_spin_lock(&lock->waitq, &node);
>
> /*
> * At the head of the wait queue now, call queue_write_3step_lock()
> @@ -260,6 +191,6 @@ void queue_write_lock_slowpath(struct qrwlock *lock)
> */
> while (!queue_write_3step_lock(lock))
> arch_mutex_cpu_relax();
> - signal_next(lock, &node);
> + mcs_spin_unlock(&lock->waitq, &node);
> }
> EXPORT_SYMBOL(queue_write_lock_slowpath);
> --
> 1.7.1
>
--
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