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

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Message-ID: <e5d85c44-ab2d-329b-fbf5-467129169011@redhat.com>
Date:   Tue, 24 Oct 2017 12:07:04 -0400
From:   Waiman Long <longman@...hat.com>
To:     Eduardo Valentin <eduval@...zon.com>,
        Peter Zijlstra <peterz@...radead.org>
Cc:     Paolo Bonzini <pbonzini@...hat.com>, rkrcmar@...hat.com,
        Jonathan Corbet <corbet@....net>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>,
        "H. Peter Anvin" <hpa@...or.com>, x86@...nel.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: [PATCH 1/1] locking/qspinlock/x86: Avoid test-and-set when
 PV_DEDICATED is set

On 10/24/2017 11:37 AM, Eduardo Valentin wrote:
> Hello Peter,
> On Tue, Oct 24, 2017 at 10:13:45AM +0200, Peter Zijlstra wrote:
>> On Mon, Oct 23, 2017 at 05:44:27PM -0700, Eduardo Valentin wrote:
>>> @@ -46,6 +48,8 @@ static inline bool virt_spin_lock(struct qspinlock *lock)
>>>  	if (!static_cpu_has(X86_FEATURE_HYPERVISOR))
>>>  		return false;
>>>  
>>> +	if (kvm_para_has_feature(KVM_FEATURE_PV_DEDICATED))
>>> +		return false;
>>>  	/*
>>>  	 * On hypervisors without PARAVIRT_SPINLOCKS support we fall
>>>  	 * back to a Test-and-Set spinlock, because fair locks have
>> This does not apply. Much has been changed here recently.
>>
>  I checked against Linus master branch before sending. Which tree/branch are you referring to / should I based this?
>
Please check the tip tree
(https://git.kernel.org/pub/scm/linux/kernel/git/tip/tip.git) which has
the latest changes in locking code.

Cheers,
Longman