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@xxxxxxxxxx>
Reviewed-by: Liran Alon <liran.alon@xxxxxxxxxx>
Signed-off-by: Nir Weiner <nir.weiner@xxxxxxxxxx>
---
arch/powerpc/kvm/book3s_hv.c | 5 ++---
virt/kvm/kvm_main.c | 10 +++++-----
2 files changed, 7 insertions(+), 8 deletions(-)
diff --git a/arch/powerpc/kvm/book3s_hv.c b/arch/powerpc/kvm/book3s_hv.c
index 29ffc99bd79b..062f3c92c871 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)
diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
index 41bdec100102..2057d7ed8c3b 100644
--- a/virt/kvm/kvm_main.c
+++ b/virt/kvm/kvm_main.c
@@ -2190,17 +2190,17 @@ void kvm_sigset_deactivate(struct kvm_vcpu *vcpu)
static void grow_halt_poll_ns(struct kvm_vcpu *vcpu)
{
- unsigned int old, val, grow;
+ unsigned int old, val, grow, grow_start;
old = val = vcpu->halt_poll_ns;
+ grow_start = READ_ONCE(halt_poll_ns_grow_start);
grow = READ_ONCE(halt_poll_ns_grow);
if (!grow)
goto out;
- if (val == 0)
- val = halt_poll_ns_grow_start;
- else
- val *= grow;
+ val *= grow;
+ if (val < grow_start)
+ val = grow_start;
if (val > halt_poll_ns)
val = halt_poll_ns;
--
2.20.1
