From 3553ae5690a84a5baae5baa329467b3df2d99f72 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 5b2300b818af..575c9a51e6ba 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);