From fe492a5cdd6e314784cf6fdc5db5f593e14c8a8b Mon Sep 17 00:00:00 2001 From: Waiman Long Date: Tue, 17 Jul 2018 17:59:27 -0400 Subject: [PATCH] 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 --- arch/x86/kernel/kvm.c | 4 ++++ 1 file changed, 4 insertions(+) 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); -- 2.39.5