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

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Date:   Wed, 6 Sep 2017 19:33:10 +0200
From:   Juergen Gross <jgross@...e.com>
To:     Waiman Long <longman@...hat.com>,
        Peter Zijlstra <peterz@...radead.org>
Cc:     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 06/09/17 18:13, Waiman Long wrote:
> 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.

Hmm, right. I'll send V3 in some minutes.


Juergen