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SubjectRe: [PATCH v2 3/7] KVM-HV: KVM Steal time implementation
On Sun, Jun 19, 2011 at 12:57:53PM +0300, Avi Kivity wrote:
> On 06/17/2011 01:20 AM, Glauber Costa wrote:
> >To implement steal time, we need the hypervisor to pass the guest information
> >about how much time was spent running other processes outside the VM.
> >This is per-vcpu, and using the kvmclock structure for that is an abuse
> >we decided not to make.
> >
> >In this patchset, I am introducing a new msr, KVM_MSR_STEAL_TIME, that
> >holds the memory area address containing information about steal time
> >
> >This patch contains the hypervisor part for it. I am keeping it separate from
> >the headers to facilitate backports to people who wants to backport the kernel
> >part but not the hypervisor, or the other way around.
> >
> >
> >
> >+#define KVM_STEAL_ALIGNMENT_BITS 5
> >+#define KVM_STEAL_VALID_BITS ((-1ULL<< (KVM_STEAL_ALIGNMENT_BITS + 1)))
> >+#define KVM_STEAL_RESERVED_MASK (((1<< KVM_STEAL_ALIGNMENT_BITS) - 1 )<< 1)
>
> Clumsy, but okay.
>
> >+static void record_steal_time(struct kvm_vcpu *vcpu)
> >+{
> >+ u64 delta;
> >+
> >+ if (vcpu->arch.st.stime&& vcpu->arch.st.this_time_out) {
>
> 0 is a valid value for stime.
>
> >+
> >+ if (unlikely(kvm_read_guest(vcpu->kvm, vcpu->arch.st.stime,
> >+ &vcpu->arch.st.steal, sizeof(struct kvm_steal_time)))) {
> >+
> >+ vcpu->arch.st.stime = 0;
> >+ return;
> >+ }
> >+
> >+ delta = (get_kernel_ns() - vcpu->arch.st.this_time_out);
> >+
> >+ vcpu->arch.st.steal.steal += delta;
> >+ vcpu->arch.st.steal.version += 2;
> >+
> >+ if (unlikely(kvm_write_guest(vcpu->kvm, vcpu->arch.st.stime,
> >+ &vcpu->arch.st.steal, sizeof(struct kvm_steal_time)))) {
> >+
> >+ vcpu->arch.st.stime = 0;
> >+ return;
> >+ }
> >+ }
> >+
> >+}
> >+
> >
> >@@ -2158,6 +2206,8 @@ void kvm_arch_vcpu_load(struct kvm_vcpu *vcpu, int cpu)
> > kvm_migrate_timers(vcpu);
> > vcpu->cpu = cpu;
> > }
> >+
> >+ record_steal_time(vcpu);
> > }
>
> This records time spent in userspace in the vcpu thread as steal
> time. Is this what we want? Or just time preempted away?

It also accounts halt time (kvm_vcpu_block) as steal time. Glauber, you
could instead use the "runnable-state-but-waiting-in-runqueue" field of
SCHEDSTATS, i forgot the exact name.



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