Commit 3553ae56 authored Jul 17, 2018 by Waiman Long Committed by Paolo Bonzini Aug 06, 2018

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>

parent 450917b6

arch/x86/kernel/kvm.c

+4 −0

Original line number	Diff line number	Diff line
		@@ -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);