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 ?
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