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Re: [Xen-devel] [PATCH v6 05/11] pvqspinlock, x86: Allow unfair spinlock in a PV guest
- To: Paolo Bonzini <pbonzini@xxxxxxxxxx>
- From: Waiman Long <waiman.long@xxxxxx>
- Date: Tue, 18 Mar 2014 23:15:25 -0400
- 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>, Alok Kataria <akataria@xxxxxxxxxx>, 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>, Steven Rostedt <rostedt@xxxxxxxxxxx>, Chris Wright <chrisw@xxxxxxxxxxxx>, Thomas Gleixner <tglx@xxxxxxxxxxxxx>, Aswin Chandramouleeswaran <aswin@xxxxxx>, Chegu Vinod <chegu_vinod@xxxxxx>, Oleg Nesterov <oleg@xxxxxxxxxx>
- Delivery-date: Wed, 19 Mar 2014 03:15:46 +0000
- List-id: Xen developer discussion <xen-devel.lists.xen.org>
On 03/18/2014 04:14 AM, Paolo Bonzini wrote:
Il 17/03/2014 20:05, Konrad Rzeszutek Wilk ha scritto:
> Measurements were done by Gleb for two guests running 2.6.32 with 16
> vcpus each, on a 16-core system. One guest ran with unfair locks,
> one guest ran with fair locks. Two kernel compilations ("time make
And when you say fair locks are you saying PV ticketlocks or generic
ticketlocks?
Generic, of course.
You should see the same values with the PV ticketlock. It is not clear
to me if this testing did include that variant of locks?
Yes, PV is fine. But up to this point of the series, we are concerned
about spinlock performance when running on an overcommitted hypervisor
that doesn't support PV spinlocks.
The unfair queue lock is designed in such a way that it will only be
activated when running in a PV guest or it won't be mergeable upstream.
So there must be some way to determine if it is running under a hypervisor.
-Longman
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