[PATCH v3 5/9] KVM-HV: use schedstats to calculate steal time

[Glauber Costa <glommer@redhat.com>]

SCHEDSTATS provide a precise source of information about time tasks
spent on a runqueue, but not running (among other things). It is
specially useful for the steal time implementation, because it doesn't
record halt time at all.

To avoid a hard dependency on schedstats, since it is possible one won't
want to record statistics about all processes running, the previous method
of time measurement on put/load vcpu is kept  for !SCHEDSTATS.

Signed-off-by: Glauber Costa <glommer@redhat.com>
CC: Rik van Riel <riel@redhat.com>
CC: Jeremy Fitzhardinge <jeremy.fitzhardinge@citrix.com>
CC: Peter Zijlstra <peterz@infradead.org>
CC: Avi Kivity <avi@redhat.com>
CC: Anthony Liguori <aliguori@us.ibm.com>
CC: Eric B Munson <emunson@mgebm.net>
CC: Marcelo Tosatti <mtosatti@redhat.com>
---
 arch/x86/kvm/x86.c |   22 ++++++++++++++++++----
 1 files changed, 18 insertions(+), 4 deletions(-)

diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index df9d274..7e87159 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -1502,7 +1502,13 @@ static void record_steal_time(struct kvm_vcpu *vcpu)
 		&vcpu->arch.st.steal, sizeof(struct kvm_steal_time))))
 		return;
 
-	delta = (get_kernel_ns() - vcpu->arch.st.this_time_out);
+#if defined(CONFIG_SCHEDSTATS) || defined(CONFIG_TASK_DELAY_ACCT)
+	if (likely(sched_info_on())) {
+		delta = current->sched_info.run_delay - vcpu->arch.st.this_time_out;
+		vcpu->arch.st.this_time_out = current->sched_info.run_delay;
+	} else 
+#endif
+		delta = (get_kernel_ns() - vcpu->arch.st.this_time_out);
 
 	vcpu->arch.st.steal.steal += delta;
 	vcpu->arch.st.steal.version += 2;
@@ -1607,9 +1613,14 @@ int kvm_set_msr_common(struct kvm_vcpu *vcpu, u32 msr, u64 data)
 							data & KVM_STEAL_VALID_BITS))
 			return 1;
 
-		vcpu->arch.st.this_time_out = get_kernel_ns();
-		record_steal_time(vcpu);
+#if defined(CONFIG_SCHEDSTATS) || defined(CONFIG_TASK_DELAY_ACCT)
+		if (likely(sched_info_on()))
+			vcpu->arch.st.this_time_out = current->sched_info.run_delay;
+		else
+#endif
+			vcpu->arch.st.this_time_out = get_kernel_ns();
 
+		record_steal_time(vcpu);
 		break;
 
 	case MSR_IA32_MCG_CTL:
@@ -2220,7 +2231,10 @@ void kvm_arch_vcpu_put(struct kvm_vcpu *vcpu)
 	kvm_x86_ops->vcpu_put(vcpu);
 	kvm_put_guest_fpu(vcpu);
 	kvm_get_msr(vcpu, MSR_IA32_TSC, &vcpu->arch.last_guest_tsc);
-	vcpu->arch.st.this_time_out = get_kernel_ns();
+#if defined(CONFIG_SCHEDSTATS) || defined(CONFIG_TASK_DELAY_ACCT)
+	if (unlikely(!sched_info_on()))
+#endif
+		vcpu->arch.st.this_time_out = get_kernel_ns();
 }
 
 static int is_efer_nx(void)
-- 
1.7.3.4