linux-kernel - Re: [PATCH v2] xen/spinlock: Don't use pvqspinlock if only 1 vCPU

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Message-ID: <a57a15cb-162f-6248-79c9-311756bd9560@oracle.com>
Date:   Tue, 31 Jul 2018 13:05:39 -0400
From:   Boris Ostrovsky <boris.ostrovsky@...cle.com>
To:     Waiman Long <longman@...hat.com>, Juergen Gross <jgross@...e.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>,
        "H. Peter Anvin" <hpa@...or.com>
Cc:     x86@...nel.org, xen-devel@...ts.xenproject.org,
        linux-kernel@...r.kernel.org,
        Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>
Subject: Re: [PATCH v2] xen/spinlock: Don't use pvqspinlock if only 1 vCPU

On 07/19/2018 05:39 PM, Waiman Long wrote:
> On a VM with only 1 vCPU, the locking fast paths will always be
> successful. In this case, there is no need to use the the PV qspinlock
> code which has higher overhead on the unlock side than the native
> qspinlock code.
>
> The xen_pvspin veriable is also turned off in this 1 vCPU case to
> eliminate unneeded pvqspinlock initialization in xen_init_lock_cpu()
> which is run after xen_init_spinlocks().
>
> Signed-off-by: Waiman Long <longman@...hat.com>


Applied to for-linus-4.19.

-boris