linux-kernel - Re: [PATCH v13 10/11] pvqspinlock, x86: Enable PV qspinlock for KVM

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Date:	Tue, 2 Dec 2014 14:10:58 -0500
From:	Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>
To:	Waiman Long <Waiman.Long@...com>
Cc:	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>,
	"H. Peter Anvin" <hpa@...or.com>,
	Peter Zijlstra <peterz@...radead.org>,
	linux-arch@...r.kernel.org, x86@...nel.org,
	linux-kernel@...r.kernel.org,
	virtualization@...ts.linux-foundation.org,
	xen-devel@...ts.xenproject.org, kvm@...r.kernel.org,
	Paolo Bonzini <paolo.bonzini@...il.com>,
	Boris Ostrovsky <boris.ostrovsky@...cle.com>,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
	Rik van Riel <riel@...hat.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Raghavendra K T <raghavendra.kt@...ux.vnet.ibm.com>,
	David Vrabel <david.vrabel@...rix.com>,
	Oleg Nesterov <oleg@...hat.com>,
	Scott J Norton <scott.norton@...com>,
	Douglas Hatch <doug.hatch@...com>
Subject: Re: [PATCH v13 10/11] pvqspinlock, x86: Enable PV qspinlock for KVM

On Wed, Oct 29, 2014 at 04:19:10PM -0400, Waiman Long wrote:
> This patch adds the necessary KVM specific code to allow KVM to
> support the CPU halting and kicking operations needed by the queue
> spinlock PV code.
> 
> Two KVM guests of 20 CPU cores (2 nodes) were created for performance
> testing in one of the following three configurations:
>  1) Only 1 VM is active
>  2) Both VMs are active and they share the same 20 physical CPUs
>     (200% overcommit)
> 
> The tests run included the disk workload of the AIM7 benchmark on
> both ext4 and xfs RAM disks at 3000 users on a 3.17 based kernel. The
> "ebizzy -m" test and futextest was was also run and its performance
> data were recorded.  With two VMs running, the "idle=poll" kernel
> option was added to simulate a busy guest. If PV qspinlock is not
> enabled, unfairlock will be used automically in a guest.

What is the unfairlock? Isn't it just using a bytelock at this point?
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