Re: Second KVM process hangs eating 80-100% CPU on host during startup

[Marcelo Tosatti <mtosatti@redhat.com>]

On Sat, Apr 19, 2008 at 03:47:31PM -0700, Alex Davis wrote:
> --- On Fri, 4/18/08, Avi Kivity <avi@qumranet.com> wrote:
> 
> > From: Avi Kivity <avi@qumranet.com>
> > Subject: Re: [kvm-devel] Second KVM process hangs eating 80-100% CPU on host during startup
> [snip]
> 
> I tried booting the guest with 'lpj=10682525' to work around the 
> calibrate_delay issue, but that gave me:
> 
> [    0.004100] ENABLING IO-APIC IRQs
> [    0.004100] ..TIMER: vector=0x31 apic1=0 pin1=0 apic2=-1 pin2=-1
> [    0.004100] ..MP-BIOS bug: 8254 timer not connected to IO-APIC
> [    0.004100] ...trying to set up timer (IRQ0) through the 8259A ... failed.
> [    0.004100] ...trying to set up timer as Virtual Wire IRQ ... failed.
> [    0.004100] ...trying to set up timer as ExtINT IRQ ... failed :(.
> [    0.004100] Kernel panic - not syncing: IO-APIC + timer doesn't work! Boot
> with apic=debug and send a report.Then try booting with the 'noapic' option.
> 
> Booting with 'apic=debug' gives these additional lines:
> [    0.004100] Getting VERSION: 50014
> [    0.004100] Getting VERSION: 50014
> [    0.004100] Getting ID: 0
> [    0.004100] Getting LVT0: 700
> [    0.004100] Getting LVT1: 10000

Hi Alex,

Can you please try the following.

KVM: PIT: make last_injected_time per-guest

Otherwise multiple guests use the same variable and boom.

Also use kvm_vcpu_kick() to make sure that if a timer triggers on 
a different CPU the event won't be missed.

Signed-off-by: Marcelo Tosatti <mtosatti@redhat.com>


diff --git a/arch/x86/kvm/i8254.c b/arch/x86/kvm/i8254.c
index 2852dd1..5697ad2 100644
--- a/arch/x86/kvm/i8254.c
+++ b/arch/x86/kvm/i8254.c
@@ -200,10 +200,8 @@ int __pit_timer_fn(struct kvm_kpit_state *ps)
 
 	atomic_inc(&pt->pending);
 	smp_mb__after_atomic_inc();
-	if (vcpu0 && waitqueue_active(&vcpu0->wq)) {
-		vcpu0->arch.mp_state = KVM_MP_STATE_RUNNABLE;
-		wake_up_interruptible(&vcpu0->wq);
-	}
+	if (vcpu0)
+		kvm_vcpu_kick(vcpu0);
 
 	pt->timer.expires = ktime_add_ns(pt->timer.expires, pt->period);
 	pt->scheduled = ktime_to_ns(pt->timer.expires);
@@ -572,7 +570,6 @@ void kvm_inject_pit_timer_irqs(struct kvm_vcpu *vcpu)
 	struct kvm_pit *pit = vcpu->kvm->arch.vpit;
 	struct kvm *kvm = vcpu->kvm;
 	struct kvm_kpit_state *ps;
-	static unsigned long last_injected_time;
 
 	if (vcpu && pit) {
 		ps = &pit->pit_state;
@@ -582,11 +579,11 @@ void kvm_inject_pit_timer_irqs(struct kvm_vcpu *vcpu)
 		 * 2. Last interrupt was accepted or waited for too long time*/
 		if (atomic_read(&ps->pit_timer.pending) &&
 		    (ps->inject_pending ||
-		    (jiffies - last_injected_time
+		    (jiffies - ps->last_injected_time
 				>= KVM_MAX_PIT_INTR_INTERVAL))) {
 			ps->inject_pending = 0;
 			__inject_pit_timer_intr(kvm);
-			last_injected_time = jiffies;
+			ps->last_injected_time = jiffies;
 		}
 	}
 }
diff --git a/arch/x86/kvm/i8254.h b/arch/x86/kvm/i8254.h
index e63ef38..db25c2a 100644
--- a/arch/x86/kvm/i8254.h
+++ b/arch/x86/kvm/i8254.h
@@ -35,6 +35,7 @@ struct kvm_kpit_state {
 	struct mutex lock;
 	struct kvm_pit *pit;
 	bool inject_pending; /* if inject pending interrupts */
+	unsigned long last_injected_time;
 };
 
 struct kvm_pit {

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