Re: [Xen-devel] [PATCH v2 1/2] paravirt/locks: use new static key for controlling call of virt_spin_lock()

[Waiman Long <longman@xxxxxxxxxx>]

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


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