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Re: [Xen-devel] [PATCH v5 1/8] qspinlock: Introducing a 4-byte queue spinlock implementation
- To: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
- From: Waiman Long <waiman.long@xxxxxx>
- Date: Thu, 27 Feb 2014 15:25:09 -0500
- Cc: Jeremy Fitzhardinge <jeremy@xxxxxxxx>, Raghavendra K T <raghavendra.kt@xxxxxxxxxxxxxxxxxx>, Boris Ostrovsky <boris.ostrovsky@xxxxxxxxxx>, virtualization@xxxxxxxxxxxxxxxxxxxxxxxxxx, Andi Kleen <andi@xxxxxxxxxxxxxx>, "H. Peter Anvin" <hpa@xxxxxxxxx>, Michel Lespinasse <walken@xxxxxxxxxx>, Alok Kataria <akataria@xxxxxxxxxx>, linux-arch@xxxxxxxxxxxxxxx, x86@xxxxxxxxxx, Ingo Molnar <mingo@xxxxxxxxxx>, Scott J Norton <scott.norton@xxxxxx>, xen-devel@xxxxxxxxxxxxxxxxxxxx, "Paul E. McKenney" <paulmck@xxxxxxxxxxxxxxxxxx>, Alexander Fyodorov <halcy@xxxxxxxxx>, Arnd Bergmann <arnd@xxxxxxxx>, Daniel J Blueman <daniel@xxxxxxxxxxxxx>, Rusty Russell <rusty@xxxxxxxxxxxxxxx>, Oleg Nesterov <oleg@xxxxxxxxxx>, Steven Rostedt <rostedt@xxxxxxxxxxx>, Chris Wright <chrisw@xxxxxxxxxxxx>, George Spelvin <linux@xxxxxxxxxxx>, Thomas Gleixner <tglx@xxxxxxxxxxxxx>, Aswin Chandramouleeswaran <aswin@xxxxxx>, Chegu Vinod <chegu_vinod@xxxxxx>, Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>, linux-kernel@xxxxxxxxxxxxxxx, David Vrabel <david.vrabel@xxxxxxxxxx>, Paolo Bonzini <pbonzini@xxxxxxxxxx>, Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>, Tim Chen <tim.c.chen@xxxxxxxxxxxxxxx>
- Delivery-date: Thu, 27 Feb 2014 20:25:43 +0000
- List-id: Xen developer discussion <xen-devel.lists.xen.org>
On 02/26/2014 11:22 AM, Peter Zijlstra wrote:
On Wed, Feb 26, 2014 at 10:14:21AM -0500, Waiman Long wrote:
+struct qnode {
+ u32 wait; /* Waiting flag */
+ struct qnode *next; /* Next queue node addr */
+};
+
+struct qnode_set {
+ struct qnode nodes[MAX_QNODES];
+ int node_idx; /* Current node to use */
+};
+
+/*
+ * Per-CPU queue node structures
+ */
+static DEFINE_PER_CPU_ALIGNED(struct qnode_set, qnset) = { {{0}}, 0 };
So I've not yet wrapped my head around any of this; and I see a later
patch adds some paravirt gunk to this, but it does blow you can't keep
it a single cacheline for the sane case.
There is a 4-byte hole in the qnode structure for x86-64. I did try to
make the additional PV fields used only 4 bytes so that there is no
increase in size in the qnode structure unless we need to support 16K
CPUs or more.
-Longman
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