KVM: Never start grow vCPU halt_poll_ns from value below halt_poll_ns_grow_start
grow_halt_poll_ns() have a strange behaviour in case
(vcpu->halt_poll_ns != 0) &&
(vcpu->halt_poll_ns < halt_poll_ns_grow_start).
In this case, vcpu->halt_poll_ns will be multiplied by grow factor
(halt_poll_ns_grow) which will require several grow iteration in order
to reach a value bigger than halt_poll_ns_grow_start.
This means that growing vcpu->halt_poll_ns from value of 0 is slower
than growing it from a positive value less than halt_poll_ns_grow_start.
Which is misleading and inaccurate.
Fix issue by changing grow_halt_poll_ns() to set vcpu->halt_poll_ns
to halt_poll_ns_grow_start in any case that
(vcpu->halt_poll_ns < halt_poll_ns_grow_start).
Regardless if vcpu->halt_poll_ns is 0.
use READ_ONCE to get a consistent number for all cases.
Reviewed-by: Boris Ostrovsky <boris.ostrovsky@oracle.com>
Reviewed-by: Liran Alon <liran.alon@oracle.com>
Signed-off-by: Nir Weiner <nir.weiner@oracle.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
diff --git a/arch/powerpc/kvm/book3s_hv.c b/arch/powerpc/kvm/book3s_hv.c
index 29ffc99..062f3c92 100644
--- a/arch/powerpc/kvm/book3s_hv.c
+++ b/arch/powerpc/kvm/book3s_hv.c
@@ -3634,10 +3634,9 @@ static void grow_halt_poll_ns(struct kvmppc_vcore *vc)
if (!halt_poll_ns_grow)
return;
- if (vc->halt_poll_ns == 0)
+ vc->halt_poll_ns *= halt_poll_ns_grow;
+ if (vc->halt_poll_ns < halt_poll_ns_grow_start)
vc->halt_poll_ns = halt_poll_ns_grow_start;
- else
- vc->halt_poll_ns *= halt_poll_ns_grow;
}
static void shrink_halt_poll_ns(struct kvmppc_vcore *vc)
