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

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Message-ID: <20171024162656.GB5007@u40b0340c692b58f6553c.ant.amazon.com>
Date:   Tue, 24 Oct 2017 09:26:56 -0700
From:   Eduardo Valentin <eduval@...zon.com>
To:     Waiman Long <longman@...hat.com>
CC:     Eduardo Valentin <eduval@...zon.com>,
        Peter Zijlstra <peterz@...radead.org>,
        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

Hey Waiman,

On Tue, Oct 24, 2017 at 12:07:04PM -0400, Waiman Long wrote:
> 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.

I will rebase the patch on top of the tip tree.

Thanks.

> 
> Cheers,
> Longman
> 

-- 
All the best,
Eduardo Valentin