From mboxrd@z Thu Jan  1 00:00:00 1970
From: Paolo Bonzini <pbonzini@redhat.com>
Subject: Re: [PATCH v6 05/11] pvqspinlock, x86: Allow unfair spinlock in a
 PV guest
Date: Wed, 19 Mar 2014 11:07:43 +0100
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To: Waiman Long <waiman.long@hp.com>
Cc: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>, Jeremy Fitzhardinge <jeremy@goop.org>, Raghavendra K T <raghavendra.kt@linux.vnet.ibm.com>, Gleb Natapov <gleb@redhat.com>, Peter Zijlstra <peterz@infradead.org>, virtualization@lists.linux-foundation.org, Andi Kleen <andi@firstfloor.org>, "H. Peter Anvin" <hpa@zytor.com>, Michel Lespinasse <walken@google.com>, Alok Kataria <akataria@vmware.com>, linux-arch@vger.kernel.org, kvm@vger.kernel.org, x86@kernel.org, Ingo Molnar <mingo@redhat.com>, xen-devel@lists.xenproject.org, "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>, Rik van Riel <riel@redhat.com>, Arnd Bergmann <arnd@arndb.de>, Scott J Norton <scott.norton@hp.com>, Steven Rostedt <rostedt@goodmis.org>, Chris Wright <chrisw@sous-sol.org>, Thomas Gleixner <tglx@linutronix.de>, Aswin Chandramouleeswaran <aswin@hp.com>, Chegu Vinod <chegu_vinod@hp.com>

Il 19/03/2014 04:15, Waiman Long ha scritto:
>>> 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.

Exactly.  What you want is boot_cpu_has(X86_FEATURE_HYPERVISOR).

Paolo