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Re: [Xen-devel] [PATCH v5 3/8] qspinlock, x86: Add x86 specific optimization for 2 contending tasks
- To: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
- From: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
- Date: Fri, 28 Feb 2014 08:25:24 -0800
- Cc: Jeremy Fitzhardinge <jeremy@xxxxxxxx>, Raghavendra K T <raghavendra.kt@xxxxxxxxxxxxxxxxxx>, Aswin Chandramouleeswaran <aswin@xxxxxx>, Andi Kleen <andi@xxxxxxxxxxxxxx>, Peter Anvin <hpa@xxxxxxxxx>, Michel Lespinasse <walken@xxxxxxxxxx>, Alok Kataria <akataria@xxxxxxxxxx>, linux-arch@xxxxxxxxxxxxxxx, the arch/x86 maintainers <x86@xxxxxxxxxx>, Ingo Molnar <mingo@xxxxxxxxxx>, Daniel J Blueman <daniel@xxxxxxxxxxxxx>, xen-devel@xxxxxxxxxxxxxxxxxxxx, Paul McKenney <paulmck@xxxxxxxxxxxxxxxxxx>, Alexander Fyodorov <halcy@xxxxxxxxx>, Arnd Bergmann <arnd@xxxxxxxx>, Scott J Norton <scott.norton@xxxxxx>, Rusty Russell <rusty@xxxxxxxxxxxxxxx>, Steven Rostedt <rostedt@xxxxxxxxxxx>, Chris Wright <chrisw@xxxxxxxxxxxx>, George Spelvin <linux@xxxxxxxxxxx>, Boris Ostrovsky <boris.ostrovsky@xxxxxxxxxx>, virtualization <virtualization@xxxxxxxxxxxxxxxxxxxxxxxxxx>, Chegu Vinod <chegu_vinod@xxxxxx>, Waiman Long <waiman.long@xxxxxx>, Oleg Nesterov <oleg@xxxxxxxxxx>, Linux Kernel Mailing List <linux-kernel@xxxxxxxxxxxxxxx>, Thomas Gleixner <tglx@xxxxxxxxxxxxx>, David Vrabel <david.vrabel@xxxxxxxxxx>, Paolo Bonzini <pbonzini@xxxxxxxxxx>, Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>, Tim Chen <tim.c.chen@xxxxxxxxxxxxxxx>
- Delivery-date: Fri, 28 Feb 2014 16:25:41 +0000
- List-id: Xen developer discussion <xen-devel.lists.xen.org>
On Feb 28, 2014 1:30 AM, "Peter Zijlstra" <peterz@xxxxxxxxxxxxx> wrote:
>
> At low contention the cmpxchg won't have to be retried (much) so using
> it won't be a problem and you get to have arbitrary atomic ops.
Peter, the difference between an atomic op and *no* atomic op is huge.
And Waiman posted numbers for the optimization. Why do you argue with handwaving and against numbers?
ÂÂÂÂÂÂ Linus
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