linux-kernel - Re: [PATCH v2 1/2] paravirt/locks: use new static key for controlling call of virt_spin

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Message-ID: <73d39808-ad47-6d06-89be-034181099408@redhat.com>
Date:   Wed, 6 Sep 2017 12:13:44 -0400
From:   Waiman Long <longman@...hat.com>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     Juergen Gross <jgross@...e.com>, linux-kernel@...r.kernel.org,
        xen-devel@...ts.xenproject.org, x86@...nel.org,
        virtualization@...ts.linux-foundation.org, jeremy@...p.org,
        chrisw@...s-sol.org, akataria@...are.com, rusty@...tcorp.com.au,
        boris.ostrovsky@...cle.com, hpa@...or.com, tglx@...utronix.de,
        mingo@...hat.com
Subject: Re: [PATCH v2 1/2] paravirt/locks: use new static key for controlling
 call of virt_spin_lock()

On 09/06/2017 12:04 PM, Peter Zijlstra wrote:
> On Wed, Sep 06, 2017 at 11:49:49AM -0400, Waiman Long wrote:
>>>  #define virt_spin_lock virt_spin_lock
>>>  static inline bool virt_spin_lock(struct qspinlock *lock)
>>>  {
>>> +	if (!static_branch_likely(&virt_spin_lock_key))
>>> +		return false;
>>>  	if (!static_cpu_has(X86_FEATURE_HYPERVISOR))
>>>  		return false;
>>>  
> Now native has two NOPs instead of one. Can't we merge these two static
> branches?


I guess we can remove the static_cpu_has() call. Just that any spin_lock
calls before native_pv_lock_init() will use the virt_spin_lock(). That
is still OK as the init call is done before SMP starts.

Cheers,
Longman