linux-kernel - Re: [PATCHv2 1/1] locking/qspinlock/x86: Avoid test-and-set when PV

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Message-ID: <45bf1347-1d88-0c2c-77cb-a75da3b01149@redhat.com>
Date:   Thu, 2 Nov 2017 14:12:13 -0400
From:   Waiman Long <longman@...hat.com>
To:     Eduardo Valentin <eduval@...zon.com>,
        Paolo Bonzini <pbonzini@...hat.com>
Cc:     rkrcmar@...hat.com, Matt Wilson <msw@...zon.com>,
        Jonathan Corbet <corbet@....net>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>,
        "H. Peter Anvin" <hpa@...or.com>, x86@...nel.org,
        Peter Zijlstra <peterz@...radead.org>, kvm@...r.kernel.org,
        linux-doc@...r.kernel.org, linux-kernel@...r.kernel.org,
        "Jan H . Schoenherr" <jschoenh@...zon.de>,
        Anthony Liguori <aliguori@...zon.com>
Subject: Re: [PATCHv2 1/1] locking/qspinlock/x86: Avoid test-and-set when
 PV_DEDICATED is set

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?

See https://lkml.org/lkml/2017/11/1/655

Cheers,
Longman