From mboxrd@z Thu Jan  1 00:00:00 1970
From: Peter Zijlstra <peterz@infradead.org>
Subject: Re: [PATCH v11 09/16] qspinlock,
 x86: Allow unfair spinlock in a virtual guest
Date: Sun, 15 Jun 2014 15:14:16 +0200
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To: Waiman Long <waiman.long@hp.com>
Cc: linux-arch@vger.kernel.org, Raghavendra K T <raghavendra.kt@linux.vnet.ibm.com>, Oleg Nesterov <oleg@redhat.com>, Gleb Natapov <gleb@redhat.com>, kvm@vger.kernel.org, Scott J Norton <scott.norton@hp.com>, x86@kernel.org, Paolo Bonzini <paolo.bonzini@gmail.com>, linux-kernel@vger.kernel.org, virtualization@lists.linux-foundation.org, Ingo Molnar <mingo@redhat.com>, Chegu Vinod <chegu_vinod@hp.com>, David Vrabel <david.vrabel@citrix.com>, "H. Peter Anvin" <hpa@zytor.com>, xen-devel@lists.xenproject.org, Thomas Gleixner <tglx@linutronix.de>, "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>, Linus Torvalds <torvalds@linux-foundation.org>, Boris Ostrovsky <boris.ostrovsky@oracle.com>
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On Thu, Jun 12, 2014 at 05:08:28PM -0400, Waiman Long wrote:
> >Native performance is king, try your very utmost bestest to preserve
> >that, paravirt is a distant second and nobody sane should care about the
> >virt case at all.
> 
> The patch won't affect native performance unless the kernel is built with
> VIRT_UNFAIR_LOCKS selected. The same is also true when PARAVIRT_SPINLOCKS is
> selected. There is no way around that.

VIRT_UNFAIR_LOCKS is an impossible switch to have; a distro cannot make
the right choice.

> I do agree that I may over-engineer on this patch,

Simple things first, then add complexity.