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

[Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx>]

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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