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x86/kvm: Don't use pvqspinlock code if only 1 vCPU 

On a VM with only 1 vCPU, the locking fast path 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.

Signed-off-by: Waiman Long <longman@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
This commit is contained in:
Waiman Long 2018-07-17 17:59:27 -04:00 committed by Paolo Bonzini
parent 450917b654
commit 3553ae5690
1 changed files with 4 additions and 0 deletions
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4
arch/x86/kernel/kvm.c
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@ -748,6 +748,10 @@ void __init kvm_spinlock_init(void)
if (kvm_para_has_hint(KVM_HINTS_REALTIME))
return;
/* Don't use the pvqspinlock code if there is only 1 vCPU. */
if (num_possible_cpus() == 1)
return;
__pv_init_lock_hash();
pv_lock_ops.queued_spin_lock_slowpath = __pv_queued_spin_lock_slowpath;
pv_lock_ops.queued_spin_unlock = PV_CALLEE_SAVE(__pv_queued_spin_unlock);