Re: [PATCH 0/2][KVM] guest time accounting

Christian Borntraeger
2007-08-13T15:22:43Z

Am Montag, 13. August 2007 schrieb Laurent Vivier:
> >> As guest accounting is hw dependent, I think we should add a hook in the
> >> accounting functions.
> >>
> >
> > Isn't PF_VM exactly such a hook? All the hypervisor needs to do is to
> > set/unset it correctly?
>
> In fact, no.
>
> PF_VM is used to know we have entered a virtual CPU (the hypervisor set it,
> the scheduler unset it on accounting)

Why not do something like the following. (This patch does not work as it
relies on the no-existing var cputime_since_last_update, but it shows the
idea)

---
drivers/kvm/kvm.h | 13 +++++++++++++
drivers/kvm/svm.c | 3 ++-
drivers/kvm/vmx.c | 3 ++-
kernel/sched.c | 1 -
4 files changed, 17 insertions(+), 3 deletions(-)

Index: kvm/drivers/kvm/kvm.h
===================================================================
--- kvm.orig/drivers/kvm/kvm.h
+++ kvm/drivers/kvm/kvm.h
@@ -8,6 +8,7 @@

#include <linux/types.h>
#include <linux/list.h>
+#include <linux/kernel_stat.h>
#include <linux/mutex.h>
#include <linux/spinlock.h>
#include <linux/signal.h>
@@ -726,6 +727,18 @@ static inline u32 get_rdx_init_val(void)
return 0x600; /* P6 family */
}

+static inline guest_enter(void)
+{
+ account_system_time(current, 0, cputime_since_last_update);
+ current->flags |= PF_VCPU;
+}
+
+static inline guest_exit(void)
+{
+ current->flags &= ~PF_VCPU;
+ account_system_time(current, 0, cputime_since_last_update);
+}
+
#define ASM_VMX_VMCLEAR_RAX ".byte 0x66, 0x0f, 0xc7, 0x30"
#define ASM_VMX_VMLAUNCH ".byte 0x0f, 0x01, 0xc2"
#define ASM_VMX_VMRESUME ".byte 0x0f, 0x01, 0xc3"
Index: kvm/kernel/sched.c
===================================================================
--- kvm.orig/kernel/sched.c
+++ kvm/kernel/sched.c
@@ -3251,7 +3251,6 @@ void account_system_time(struct task_str
p->utime = cputime_add(p->utime, cputime);
cpustat->user = cputime64_add(cpustat->user, tmp);
cpustat->guest = cputime64_add(cpustat->guest, tmp);
- p->flags &= ~PF_VCPU;
return;
}

Index: kvm/drivers/kvm/svm.c
===================================================================
--- kvm.orig/drivers/kvm/svm.c
+++ kvm/drivers/kvm/svm.c
@@ -1404,7 +1404,7 @@ again:
clgi();

vcpu->guest_mode = 1;
- current->flags |= PF_VCPU;
+ guest_enter();
if (vcpu->requests)
if (test_and_clear_bit(KVM_TLB_FLUSH, &vcpu->requests))
svm_flush_tlb(vcpu);
@@ -1537,6 +1537,7 @@ again:
#endif
: "cc", "memory" );

+ guest_exit();
vcpu->guest_mode = 0;

if (vcpu->fpu_active) {
Index: kvm/drivers/kvm/vmx.c
===================================================================
--- kvm.orig/drivers/kvm/vmx.c
+++ kvm/drivers/kvm/vmx.c
@@ -2078,7 +2078,7 @@ again:
local_irq_disable();

vcpu->guest_mode = 1;
- current->flags |= PF_VCPU;
+ guest_enter();
if (vcpu->requests)
if (test_and_clear_bit(KVM_TLB_FLUSH, &vcpu->requests))
vmx_flush_tlb(vcpu);
@@ -2199,6 +2199,7 @@ again:
[cr2]"i"(offsetof(struct kvm_vcpu, cr2))
: "cc", "memory" );

+ guest_exit();
vcpu->guest_mode = 0;
local_irq_enable();