path: root/virt
diff options
authorNir Weiner <nir.weiner@oracle.com>2019-01-27 12:17:16 +0200
committerPaolo Bonzini <pbonzini@redhat.com>2019-02-20 22:48:51 +0100
commitdee339b5c1da3e6fa139b97f74f99dc9f0b03ff6 (patch)
tree6693b07487412d7ca10a17cf07d31dcdb9d43fe0 /virt
parent49113d360bdeb4dd916fb6bffbcc3e157422b6fd (diff)
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>
Diffstat (limited to 'virt')
1 files changed, 5 insertions, 5 deletions
diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
index ae818d27a1a4..5087cf703ed1 100644
--- a/virt/kvm/kvm_main.c
+++ b/virt/kvm/kvm_main.c
@@ -2189,17 +2189,17 @@ 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;