From: Waiman Long Date: Tue, 17 Jul 2018 21:59:27 +0000 (-0400) Subject: x86/kvm: Don't use pvqspinlock code if only 1 vCPU X-Git-Url: http://git.maquefel.me/?a=commitdiff_plain;h=3553ae5690a84a5baae5baa329467b3df2d99f72;p=linux.git 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 Signed-off-by: Paolo Bonzini --- diff --git a/arch/x86/kernel/kvm.c b/arch/x86/kernel/kvm.c index 5b2300b818af9..575c9a51e6ba9 100644 --- a/arch/x86/kernel/kvm.c +++ b/arch/x86/kernel/kvm.c @@ -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);