On Tue, Jul 17, 2018 at 05:59:27PM -0400, Waiman Long wrote: > 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.
Why not make this global? That is for both KVM and Xen and any other virtualized guest that uses this? > > Signed-off-by: Waiman Long <long...@redhat.com> > --- > 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 5b2300b..575c9a5 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); > -- > 1.8.3.1 >
