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Re: [Xen-devel] [PATCH v5 2/8] qspinlock, x86: Enable x86-64 to use queue spinlock
- To: Oleg Nesterov <oleg@xxxxxxxxxx>
- From: Waiman Long <waiman.long@xxxxxx>
- Date: Tue, 04 Mar 2014 10:06:07 -0500
- Cc: Jeremy Fitzhardinge <jeremy@xxxxxxxx>, Raghavendra K T <raghavendra.kt@xxxxxxxxxxxxxxxxxx>, kvm@xxxxxxxxxxxxxxx, Peter Zijlstra <peterz@xxxxxxxxxxxxx>, virtualization@xxxxxxxxxxxxxxxxxxxxxxxxxx, Andi Kleen <andi@xxxxxxxxxxxxxx>, "H. Peter Anvin" <hpa@xxxxxxxxx>, Michel Lespinasse <walken@xxxxxxxxxx>, Thomas Gleixner <tglx@xxxxxxxxxxxxx>, linux-arch@xxxxxxxxxxxxxxx, Gleb Natapov <gleb@xxxxxxxxxx>, x86@xxxxxxxxxx, Ingo Molnar <mingo@xxxxxxxxxx>, xen-devel@xxxxxxxxxxxxxxxxxxxx, "Paul E. McKenney" <paulmck@xxxxxxxxxxxxxxxxxx>, Arnd Bergmann <arnd@xxxxxxxx>, Scott J Norton <scott.norton@xxxxxx>, Rusty Russell <rusty@xxxxxxxxxxxxxxx>, Steven Rostedt <rostedt@xxxxxxxxxxx>, Chris Wright <chrisw@xxxxxxxxxxxx>, Alok Kataria <akataria@xxxxxxxxxx>, Aswin Chandramouleeswaran <aswin@xxxxxx>, Chegu Vinod <chegu_vinod@xxxxxx>, Boris Ostrovsky <boris.ostrovsky@xxxxxxxxxx>, linux-kernel@xxxxxxxxxxxxxxx, David Vrabel <david.vrabel@xxxxxxxxxx>, Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>, Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
- Delivery-date: Tue, 04 Mar 2014 15:06:37 +0000
- List-id: Xen developer discussion <xen-devel.lists.xen.org>
On 03/02/2014 09:10 AM, Oleg Nesterov wrote:
On 02/26, Waiman Long wrote:
+#define _ARCH_SUPPORTS_ATOMIC_8_16_BITS_OPS
+
+/*
+ * x86-64 specific queue spinlock union structure
+ */
+union arch_qspinlock {
+ struct qspinlock slock;
+ u8 lock; /* Lock bit */
+};
And this enables the optimized version of queue_spin_setlock().
But why does it check ACCESS_ONCE(qlock->lock) == 0 ? This is called
right after queue_get_lock_qcode() returns 0, this locked should be
likely unlocked.
Oleg.
Yes, the read check in queue_spin_setlock is probably redundant. Will
remove that.
-Longman
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