On Tue, Jun 28, 2011 at 09:30:29AM -0300, Glauber Costa wrote:
> On 06/20/2011 05:56 PM, Marcelo Tosatti wrote:
> >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.
> >
> I thought about it in the past. I let the idea aside because I
> didn't want to introduce a dependency on SCHEDSTATS. But thinking
> about it again now (and after some days of experimentations with
> it), I think we could have both.
>
> use run_delay (the field you were thinking of) when schedstats are
> available, and fallback to an estimate method like the one we're
> doing when it is not.
>
> Objections ?
I'm okay with that.
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