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Date:   Thu, 2 Nov 2017 14:12:13 -0400
From:   Waiman Long <>
To:     Eduardo Valentin <>,
        Paolo Bonzini <>
Cc:, Matt Wilson <>,
        Jonathan Corbet <>,
        Thomas Gleixner <>,
        Ingo Molnar <>,
        "H. Peter Anvin" <>,,
        Peter Zijlstra <>,,,,
        "Jan H . Schoenherr" <>,
        Anthony Liguori <>
Subject: Re: [PATCHv2 1/1] locking/qspinlock/x86: Avoid test-and-set when

On 11/02/2017 02:08 PM, Eduardo Valentin wrote:
> On Thu, Nov 02, 2017 at 06:56:46PM +0100, Paolo Bonzini wrote:
>> On 02/11/2017 18:45, Eduardo Valentin wrote:
>>> Currently, the existing qspinlock implementation will fallback to
>>> test-and-set if the hypervisor has not set the PV_UNHALT flag.
>>> This patch gives the opportunity to guest kernels to select
>>> between test-and-set and the regular queueu fair lock implementation
>>> based on the PV_DEDICATED KVM feature flag. When the PV_DEDICATED
>>> flag is not set, the code will still fall back to test-and-set,
>>> but when the PV_DEDICATED flag is set, the code will use
>>> the regular queue spinlock implementation.
>> Have you seen Waiman's series that lets you specify this on the guest
>> command line instead?  Would this be acceptable for your use case?
> No, can you please share a link to it? is it already merged to tip/master?



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