From dee339b5c1da3e6fa139b97f74f99dc9f0b03ff6 Mon Sep 17 00:00:00 2001 From: Nir Weiner Date: Sun, 27 Jan 2019 12:17:16 +0200 Subject: [PATCH] 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 Reviewed-by: Liran Alon Signed-off-by: Nir Weiner Signed-off-by: Paolo Bonzini --- 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 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;