[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]
Re: [Xen-devel] [PATCH v5 1/8] qspinlock: Introducing a 4-byte queue spinlock implementation
- To: Oleg Nesterov <oleg@xxxxxxxxxx>
- From: Waiman Long <waiman.long@xxxxxx>
- Date: Tue, 04 Mar 2014 09:58:14 -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 14:59:00 +0000
- List-id: Xen developer discussion <xen-devel.lists.xen.org>
On 03/02/2014 08:31 AM, Oleg Nesterov wrote:
Forgot to ask...
On 02/26, Waiman Long wrote:
+notify_next:
+ /*
+ * Wait, if needed, until the next one in queue set up the next field
+ */
+ while (!(next = ACCESS_ONCE(node->next)))
+ arch_mutex_cpu_relax();
+ /*
+ * The next one in queue is now at the head
+ */
+ smp_store_release(&next->wait, false);
Do we really need smp_store_release()? It seems that we can rely on the
control dependency here. And afaics there is no need to serialise this
store with other changes in *lock, plus they all have mb's anyway.
Oleg.
I am just following the current logic in the mcs_spin_unlock function.
It is probably true that we don't need the release semantic in this
particular case.
-Longman
_______________________________________________
Xen-devel mailing list
Xen-devel@xxxxxxxxxxxxx
http://lists.xen.org/xen-devel
|
