Fix guest eating 100% cpu when guest is idle on PowerPC

* This update consolidates patches, adds more explicit comments, and add wait check when rfi instruction is emulated.

This set of patches fixes 100% CPU usage when a guest is idle on PowerPC. Idle CPU usage is now at ~15-16% CPU time. An improvment.

4 files changed, 91 insertions(+), 4 deletions(-)
arch/powerpc/kvm/emulate.c          |   14 +++++++
arch/powerpc/kvm/powerpc.c          |   12 ++++--
arch/powerpc/platforms/44x/Makefile |    2 -
arch/powerpc/platforms/44x/idle.c   |   67 +++++++++++++++++++++++++++++++++++

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2 files changed, 68 insertions(+), 1 deletion(-)

arch/powerpc/platforms/44x/Makefile | 2 -
arch/powerpc/platforms/44x/idle.c | 67 +++++++++++++++++++++++++++++++++++

This patch has been accepted upstream and will be in 2.6.26. So it will eventually need to be removed when we move to 2.6.26rc.

This patch adds the ability for the CPU to go into wait state while in cpu_idle loop. This helps virtulization solutions know when the guest Linux kernel is in an idle state. There are two ways to do it.

Command line options:
idle=spin <-- CPU will spin

By default will go into wait mode.

@@ -1,4 +1,4 @@ obj-$(CONFIG_44x)	:= misc_44x.o
-obj-$(CONFIG_44x)	:= misc_44x.o
+obj-$(CONFIG_44x)	:= misc_44x.o idle.o
 obj-$(CONFIG_EBONY)	+= ebony.o
 obj-$(CONFIG_TAISHAN)	+= taishan.o
 obj-$(CONFIG_BAMBOO)	+= bamboo.o

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2 files changed, 23 insertions(+), 3 deletions(-)
arch/powerpc/kvm/emulate.c |   14 ++++++++++++++
arch/powerpc/kvm/powerpc.c |   12 +++++++++---

This patch handles a guest that is in a wait state & wake up guest that end up being recheduled and go to sleep. This ensures that the guest is not allways eating up 100% cpu when it is idle.

@@ -235,6 +235,13 @@ int kvmppc_emulate_instruction(struct kv
 		case 50:                                        /* rfi */
 			kvmppc_emul_rfi(vcpu);
 			advance = 0;
+			
+			/* Handle guest vcpu that is in wait state. 
+ 			 * This will implicitly wake up when it is ready.
+ 			 */
+			if (vcpu->arch.msr & MSR_WE) {
+				kvm_vcpu_block(vcpu);
+			}
 			break;
 
 		default:

@@ -265,6 +272,13 @@ int kvmppc_emulate_instruction(struct kv
 		case 146:                                       /* mtmsr */
 			rs = get_rs(inst);
 			kvmppc_set_msr(vcpu, vcpu->arch.gpr[rs]);
+			
+			/* Handle guest vcpu that is in wait state
+			 * This will implicitly wake up when it is ready.
+ 			 */
+			if (vcpu->arch.msr & MSR_WE) {
+				kvm_vcpu_block(vcpu);
+			}
 			break;
 
 		case 163:                                       /* wrteei */

@@ -36,13 +36,12 @@ gfn_t unalias_gfn(struct kvm *kvm, gfn_t
 
 int kvm_cpu_has_interrupt(struct kvm_vcpu *v)
 {
-	/* XXX implement me */
-	return 0;
+	return !!(v->arch.pending_exceptions);
 }
 
 int kvm_arch_vcpu_runnable(struct kvm_vcpu *v)
 {
-	return 1;
+	return !(v->arch.msr & MSR_WE);
 }
 
 

@@ -213,6 +212,9 @@ static void kvmppc_decrementer_func(unsi
 {
 	struct kvm_vcpu *vcpu = (struct kvm_vcpu *)data;
 
+	if (waitqueue_active(&vcpu->wq))
+		wake_up_interruptible(&vcpu->wq);
+
 	kvmppc_queue_exception(vcpu, BOOKE_INTERRUPT_DECREMENTER);
 }
 

@@ -339,6 +341,8 @@ int kvm_arch_vcpu_ioctl_run(struct kvm_v
 	int r;
 	sigset_t sigsaved;
 
+	vcpu_load(vcpu);
+
 	if (vcpu->sigset_active)
 		sigprocmask(SIG_SETMASK, &vcpu->sigset, &sigsaved);
 

@@ -362,6 +366,8 @@ int kvm_arch_vcpu_ioctl_run(struct kvm_v
 
 	if (vcpu->sigset_active)
 		sigprocmask(SIG_SETMASK, &sigsaved, NULL);
+
+	vcpu_put(vcpu);
 
 	return r;
 }

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