On Wed, May 04, 2022, Jon Kohler wrote: > The trace point in record_steal_time() is above the conditional > that fires kvm_vcpu_flush_tlb_guest(), so even when we might > not be flushing tlb, we still record that we are. No, it records whether not a TLB flush is needed. > Fix by nestling trace_kvm_pv_tlb_flush() under appropriate > conditional. This results in the stats for kvm:kvm_pv_tlb_flush, > as trivially observable by perf stat -e "kvm:*" -a sleep Xs, in > reporting the amount of times we actually do a pv tlb flush, > instead of just the amount of times we happen to call > record_steal_time(). > > Signed-off-by: Jon Kohler <jon@xxxxxxxxxxx> > --- > arch/x86/kvm/x86.c | 4 ++-- > 1 file changed, 2 insertions(+), 2 deletions(-) > > diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c > index 4790f0d7d40b..8d4e0e58ec34 100644 > --- a/arch/x86/kvm/x86.c > +++ b/arch/x86/kvm/x86.c > @@ -3410,9 +3410,9 @@ static void record_steal_time(struct kvm_vcpu *vcpu) > > vcpu->arch.st.preempted = 0; > > - trace_kvm_pv_tlb_flush(vcpu->vcpu_id, > - st_preempted & KVM_VCPU_FLUSH_TLB); > if (st_preempted & KVM_VCPU_FLUSH_TLB) > + trace_kvm_pv_tlb_flush(vcpu->vcpu_id, > + st_preempted & KVM_VCPU_FLUSH_TLB); If you're going to trace only when a flush is needed, this should simply be: trace_kvm_pv_tlb_flush(vcpu->vcpu_id); I haven't used this tracepoint often (at all?) so I don't have a strong preference, but I can see the "no TLB flush needed" information being extremely valuable when debugging a supsected TLB flushing bug. > kvm_vcpu_flush_tlb_guest(vcpu); > > if (!user_access_begin(st, sizeof(*st))) > -- > 2.30.1 (Apple Git-130) >
