Re: [Qemu-devel] [question] e1000 interrupt storm happenedbecauseofits correspondingioapic->irr bit always set

["Zhang Haoyu" <zhanghy@sangfor.com>]

Hi Jason,
I tested below patch, it's okay, the e1000 interrupt storm disappeared.
But I am going to make a bit change on it, could you help review it?

>Currently, we call ioapic_service() immediately when we find the irq is still
>active during eoi broadcast. But for real hardware, there's some dealy between
>the EOI writing and irq delivery (system bus latency?). So we need to emulate
>this behavior. Otherwise, for a guest who haven't register a proper irq handler
>, it would stay in the interrupt routine as this irq would be re-injected
>immediately after guest enables interrupt. This would lead guest can't move
>forward and may miss the possibility to get proper irq handler registered (one
>example is windows guest resuming from hibernation).
>
>As there's no way to differ the unhandled irq from new raised ones, this patch
>solve this problems by scheduling a delayed work when the count of irq injected
>during eoi broadcast exceeds a threshold value. After this patch, the guest can
>move a little forward when there's no suitable irq handler in case it may
>register one very soon and for guest who has a bad irq detection routine ( such
>as note_interrupt() in linux ), this bad irq would be recognized soon as in the
>past.
>
>Signed-off-by: Jason Wang <jasowang <at> redhat.com>
>---
> virt/kvm/ioapic.c |   47 +++++++++++++++++++++++++++++++++++++++++++++--
> virt/kvm/ioapic.h |    2 ++
> 2 files changed, 47 insertions(+), 2 deletions(-)
>
>diff --git a/virt/kvm/ioapic.c b/virt/kvm/ioapic.c
>index dcaf272..892253e 100644
>--- a/virt/kvm/ioapic.c
>+++ b/virt/kvm/ioapic.c
> <at>  <at>  -221,6 +221,24  <at>  <at>  int kvm_ioapic_set_irq(struct kvm_ioapic *ioapic, int irq, int level)
> 	return ret;
> }
>
>+static void kvm_ioapic_eoi_inject_work(struct work_struct *work)
>+{
>+	int i, ret;
>+	struct kvm_ioapic *ioapic = container_of(work, struct kvm_ioapic,
>+						 eoi_inject.work);
>+	spin_lock(&ioapic->lock);
>+	for (i = 0; i < IOAPIC_NUM_PINS; i++) {
>+		union kvm_ioapic_redirect_entry *ent = &ioapic->redirtbl[i];
>+
>+		if (ent->fields.trig_mode != IOAPIC_LEVEL_TRIG)
>+			continue;
>+
>+		if (ioapic->irr & (1 << i) && !ent->fields.remote_irr)
>+			ret = ioapic_service(ioapic, i);
>+	}
>+	spin_unlock(&ioapic->lock);
>+}
>+
> static void __kvm_ioapic_update_eoi(struct kvm_ioapic *ioapic, int vector,
> 				     int trigger_mode)
> {
> <at>  <at>  -249,8 +267,29  <at>  <at>  static void __kvm_ioapic_update_eoi(struct kvm_ioapic *ioapic, int vector,
>
> 		ASSERT(ent->fields.trig_mode == IOAPIC_LEVEL_TRIG);
> 		ent->fields.remote_irr = 0;
>-		if (!ent->fields.mask && (ioapic->irr & (1 << i)))
>-			ioapic_service(ioapic, i);
>+		if (!ent->fields.mask && (ioapic->irr & (1 << i))) {
>+			++ioapic->irq_eoi;
-+			++ioapic->irq_eoi;
++		    ++ioapic->irq_eoi[i];
>+			if (ioapic->irq_eoi == 100) {
-+			if (ioapic->irq_eoi == 100) {
++			if (ioapic->irq_eoi[i] == 100) {
>+				/*
>+				 * Real hardware does not deliver the irq so
>+				 * immediately during eoi broadcast, so we need
>+				 * to emulate this behavior. Otherwise, for
>+				 * guests who has not registered handler of a
>+				 * level irq, this irq would be injected
>+				 * immediately after guest enables interrupt
>+				 * (which happens usually at the end of the
>+				 * common interrupt routine). This would lead
>+				 * guest can't move forward and may miss the
>+				 * possibility to get proper irq handler
>+				 * registered. So we need to give some breath to
>+				 * guest. TODO: 1 is too long?
>+				 */
>+				schedule_delayed_work(&ioapic->eoi_inject, 1);
>+				ioapic->irq_eoi = 0;
-+				ioapic->irq_eoi = 0;
++				ioapic->irq_eoi[i] = 0;
>+			} else {
>+				ioapic_service(ioapic, i);
>+			}
>+		}
++		else {
++			ioapic->irq_eoi[i] = 0;
++		}
> 	}
> }
I think ioapic->irq_eoi is prone to reach to 100, because during a eoi broadcast, 
it's possible that another interrupt's (not current eoi's corresponding interrupt) irr is set, so the ioapic->irq_eoi will grow continually,
and not too long, ioapic->irq_eoi will reach to 100.
I want to add "u32 irq_eoi[IOAPIC_NUM_PINS];" instead of "u32 irq_eoi;".
Any ideas?

Zhang Haoyu
>
> <at>  <at>  -375,12 +414,14  <at>  <at>  void kvm_ioapic_reset(struct kvm_ioapic *ioapic)
> {
> 	int i;
>
>+	cancel_delayed_work_sync(&ioapic->eoi_inject);
> 	for (i = 0; i < IOAPIC_NUM_PINS; i++)
> 		ioapic->redirtbl[i].fields.mask = 1;
> 	ioapic->base_address = IOAPIC_DEFAULT_BASE_ADDRESS;
> 	ioapic->ioregsel = 0;
> 	ioapic->irr = 0;
> 	ioapic->id = 0;
>+	ioapic->irq_eoi = 0;
-+	ioapic->irq_eoi = 0;
++	memset(ioapic->irq_eoi, 0x00, IOAPIC_NUM_PINS);
> 	update_handled_vectors(ioapic);
> }
>
> <at>  <at>  -398,6 +439,7  <at>  <at>  int kvm_ioapic_init(struct kvm *kvm)
> 	if (!ioapic)
> 		return -ENOMEM;
> 	spin_lock_init(&ioapic->lock);
>+	INIT_DELAYED_WORK(&ioapic->eoi_inject, kvm_ioapic_eoi_inject_work);
> 	kvm->arch.vioapic = ioapic;
> 	kvm_ioapic_reset(ioapic);
> 	kvm_iodevice_init(&ioapic->dev, &ioapic_mmio_ops);
> <at>  <at>  -418,6 +460,7  <at>  <at>  void kvm_ioapic_destroy(struct kvm *kvm)
> {
> 	struct kvm_ioapic *ioapic = kvm->arch.vioapic;
>
>+	cancel_delayed_work_sync(&ioapic->eoi_inject);
> 	if (ioapic) {
> 		kvm_io_bus_unregister_dev(kvm, KVM_MMIO_BUS, &ioapic->dev);
> 		kvm->arch.vioapic = NULL;
>diff --git a/virt/kvm/ioapic.h b/virt/kvm/ioapic.h
>index 0b190c3..8938e66 100644
>--- a/virt/kvm/ioapic.h
>+++ b/virt/kvm/ioapic.h
> <at>  <at>  -47,6 +47,8  <at>  <at>  struct kvm_ioapic {
> 	void (*ack_notifier)(void *opaque, int irq);
> 	spinlock_t lock;
> 	DECLARE_BITMAP(handled_vectors, 256);
>+	struct delayed_work eoi_inject;
>+	u32 irq_eoi;
-+	u32 irq_eoi;
++	u32 irq_eoi[IOAPIC_NUM_PINS];
> };
>
> #ifdef DEBUG