From: Peter Zijlstra <peterz@infradead.org>
To: Alex Kogan <alex.kogan@oracle.com>
Cc: linux@armlinux.org.uk, mingo@redhat.com, will.deacon@arm.com,
arnd@arndb.de, longman@redhat.com, linux-arch@vger.kernel.org,
linux-arm-kernel@lists.infradead.org,
linux-kernel@vger.kernel.org, tglx@linutronix.de, bp@alien8.de,
hpa@zytor.com, x86@kernel.org, steven.sistare@oracle.com,
daniel.m.jordan@oracle.com, dave.dice@oracle.com,
rahul.x.yadav@oracle.com
Subject: Re: [PATCH v2 3/5] locking/qspinlock: Introduce CNA into the slow path of qspinlock
Date: Mon, 1 Apr 2019 11:21:15 +0200 [thread overview]
Message-ID: <20190401092115.GH11158@hirez.programming.kicks-ass.net> (raw)
In-Reply-To: <20190329152006.110370-4-alex.kogan@oracle.com>
On Fri, Mar 29, 2019 at 11:20:04AM -0400, Alex Kogan wrote:
> +static inline void pass_mcs_lock(struct mcs_spinlock *node,
> + struct mcs_spinlock *next)
> +{
> + struct mcs_spinlock *succ = NULL;
> +
> + succ = find_successor(node);
> +
> + if (succ) {
> + arch_mcs_spin_unlock_contended(&succ->locked, node->locked);
> + } else if (node->locked > 1) {
> + /*
> + * If the secondary queue is not empty, pass the lock
> + * to the first node in that queue.
> + */
> + succ = MCS_NODE(node->locked);
> + succ->tail->next = next;
> + arch_mcs_spin_unlock_contended(&succ->locked, 1);
> + } else {
> + /*
> + * Otherwise, pass the lock to the immediate successor
> + * in the main queue.
> + */
> + arch_mcs_spin_unlock_contended(&next->locked, 1);
> + }
> +}
Note that something like:
static inline void
pass_mcs_lock(struct mcs_spinlock *node, struct mcs_spinlock *next)
{
struct mcs_spinlock *succ = NULL;
uintptr_t *var = &next->locked;
uintptr_t val = 1;
succ = find_successor(node);
if (succ) {
var = &succ->locked;
val = node->locked;
} else if (node->locked > 1) {
succ = MCS_NODE(node->locked);
succ->tail->next = next; /* WRITE_ONCE() !?!? */
var = &node->locked;
}
arch_mcs_spin_unlock_contended(var, val);
}
is shorter and generates much better code if
arch_mcs_spin_unlock_contended() is asm volatile ().
next prev parent reply other threads:[~2019-04-01 9:21 UTC|newest]
Thread overview: 38+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-03-29 15:20 [PATCH v2 0/5] Add NUMA-awareness to qspinlock Alex Kogan
2019-03-29 15:20 ` [PATCH v2 1/5] locking/qspinlock: Make arch_mcs_spin_unlock_contended more generic Alex Kogan
2019-03-29 15:20 ` [PATCH v2 2/5] locking/qspinlock: Refactor the qspinlock slow path Alex Kogan
2019-03-29 15:20 ` [PATCH v2 3/5] locking/qspinlock: Introduce CNA into the slow path of qspinlock Alex Kogan
2019-04-01 9:06 ` Peter Zijlstra
2019-04-01 9:33 ` Peter Zijlstra
2019-04-03 15:53 ` Alex Kogan
2019-04-03 16:10 ` Peter Zijlstra
2019-04-01 9:21 ` Peter Zijlstra [this message]
2019-04-01 14:36 ` Waiman Long
2019-04-02 9:43 ` Peter Zijlstra
2019-04-03 15:39 ` Alex Kogan
2019-04-03 15:48 ` Waiman Long
2019-04-03 16:01 ` Peter Zijlstra
2019-04-04 5:05 ` Juergen Gross
2019-04-04 9:38 ` Peter Zijlstra
2019-04-04 18:03 ` Waiman Long
2019-06-04 23:21 ` Alex Kogan
2019-06-05 20:40 ` Peter Zijlstra
2019-06-06 15:21 ` Alex Kogan
2019-06-06 15:32 ` Waiman Long
2019-06-06 15:42 ` Waiman Long
2019-04-03 16:33 ` Waiman Long
2019-04-03 17:16 ` Peter Zijlstra
2019-04-03 17:40 ` Waiman Long
2019-04-04 2:02 ` Hanjun Guo
2019-04-04 3:14 ` Alex Kogan
2019-06-11 4:22 ` liwei (GF)
2019-06-12 4:38 ` Alex Kogan
2019-06-12 15:05 ` Waiman Long
2019-03-29 15:20 ` [PATCH v2 4/5] locking/qspinlock: Introduce starvation avoidance into CNA Alex Kogan
2019-04-02 10:37 ` Peter Zijlstra
2019-04-03 17:06 ` Alex Kogan
2019-03-29 15:20 ` [PATCH v2 5/5] locking/qspinlock: Introduce the shuffle reduction optimization " Alex Kogan
2019-04-01 9:09 ` [PATCH v2 0/5] Add NUMA-awareness to qspinlock Peter Zijlstra
2019-04-03 17:13 ` Alex Kogan
2019-07-03 11:58 ` Jan Glauber
2019-07-12 8:12 ` Hanjun Guo
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