Re: [PATCH 10/10] Change irq routing table to use gsi indexed array.

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On Wed, Jul 15, 2009 at 11:52:24PM +0300, Gleb Natapov wrote:
> On Wed, Jul 15, 2009 at 03:18:00PM -0300, Marcelo Tosatti wrote:
> > On Tue, Jul 14, 2009 at 05:30:45PM +0300, Gleb Natapov wrote:
> > > Use gsi indexed array instead of scanning all entries on each interrupt
> > > injection. Also maintain back mapping from irqchip/pin to gsi to speedup
> > > interrupt acknowledgment notifications.
> > > 
> > > Signed-off-by: Gleb Natapov <gleb@xxxxxxxxxx>
> > > ---
> > >  include/linux/kvm_host.h |   11 ++++++-
> > >  virt/kvm/irq_comm.c      |   62 ++++++++++++++++++++++++++++-----------------
> > >  2 files changed, 47 insertions(+), 26 deletions(-)
> > > 
> > > diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h
> > > index aa64d0d..ae6cbf1 100644
> > > --- a/include/linux/kvm_host.h
> > > +++ b/include/linux/kvm_host.h
> > > @@ -128,7 +128,14 @@ struct kvm_kernel_irq_routing_entry {
> > >  		} irqchip;
> > >  		struct msi_msg msi;
> > >  	};
> > > -	struct list_head link;
> > > +	struct hlist_node link;
> > > +};
> > > +
> > > +struct kvm_irq_routing_table {
> > > +	int chip[3][KVM_IOAPIC_NUM_PINS];
> > > +	struct kvm_kernel_irq_routing_entry *rt_entries;
> > > +	u32 max_gsi;
> > > +	struct hlist_head map[0];
> > >  };
> > >  
> > >  struct kvm {
> > > @@ -165,7 +172,7 @@ struct kvm {
> > >  #endif
> > >  
> > >  #ifdef CONFIG_HAVE_KVM_IRQCHIP
> > > -	struct kvm_kernel_irq_routing_entry *irq_routing;
> > > +	struct kvm_irq_routing_table *irq_routing;
> > >  	spinlock_t irq_routing_lock;
> > >  	struct hlist_head mask_notifier_list;
> > >  	struct hlist_head irq_ack_notifier_list;
> > > diff --git a/virt/kvm/irq_comm.c b/virt/kvm/irq_comm.c
> > > index c54a28b..da643d4 100644
> > > --- a/virt/kvm/irq_comm.c
> > > +++ b/virt/kvm/irq_comm.c
> > > @@ -125,6 +125,8 @@ int kvm_set_irq(struct kvm *kvm, int irq_source_id, int irq, int level)
> > >  	struct kvm_kernel_irq_routing_entry *e;
> > >  	unsigned long *irq_state, sig_level;
> > >  	int ret = -1;
> > > +	struct kvm_irq_routing_table *irq_rt;
> > > +	struct hlist_node *n;
> > >  
> > >  	trace_kvm_set_irq(irq, level, irq_source_id);
> > >  
> > > @@ -147,14 +149,13 @@ int kvm_set_irq(struct kvm *kvm, int irq_source_id, int irq, int level)
> > >  	 * writes to the unused one.
> > >  	 */
> > >  	rcu_read_lock();
> > > -	for (e = rcu_dereference(kvm->irq_routing); e && e->set; e++) {
> > > -		if (e->gsi == irq) {
> > > -			int r = e->set(e, kvm, sig_level);
> > > -			if (r < 0)
> > > -				continue;
> > > +	irq_rt = rcu_dereference(kvm->irq_routing);
> > > +	hlist_for_each_entry(e, n, &irq_rt->map[irq], link) {
> > > +		int r = e->set(e, kvm, sig_level);
> > > +		if (r < 0)
> > > +			continue;
> > >  
> > > -			ret = r + ((ret < 0) ? 0 : ret);
> > > -		}
> > > +		ret = r + ((ret < 0) ? 0 : ret);
> > >  	}
> > >  	rcu_read_unlock();
> > >  	return ret;
> > > @@ -162,21 +163,16 @@ int kvm_set_irq(struct kvm *kvm, int irq_source_id, int irq, int level)
> > >  
> > >  void kvm_notify_acked_irq(struct kvm *kvm, unsigned irqchip, unsigned pin)
> > >  {
> > > -	struct kvm_kernel_irq_routing_entry *e;
> > >  	struct kvm_irq_ack_notifier *kian;
> > >  	struct hlist_node *n;
> > > -	unsigned gsi = pin;
> > > +	unsigned gsi;
> > >  
> > >  	trace_kvm_ack_irq(irqchip, pin);
> > >  
> > >  	rcu_read_lock();
> > > -	for (e = rcu_dereference(kvm->irq_routing); e && e->set; e++) {
> > > -		if (e->irqchip.irqchip == irqchip &&
> > > -		    e->irqchip.pin == pin) {
> > > -			gsi = e->gsi;
> > > -			break;
> > > -		}
> > > -	}
> > > +	gsi = rcu_dereference(kvm->irq_routing)->chip[irqchip][pin];
> > > +	if (gsi == -1)
> > > +		gsi = pin;
> > >  
> > >  	hlist_for_each_entry_rcu(kian, n, &kvm->irq_ack_notifier_list, link)
> > >  		if (kian->gsi == gsi)
> > > @@ -277,7 +273,8 @@ void kvm_free_irq_routing(struct kvm *kvm)
> > >  	kfree(kvm->irq_routing);
> > >  }
> > >  
> > > -static int setup_routing_entry(struct kvm_kernel_irq_routing_entry *e,
> > > +static int setup_routing_entry(struct kvm_irq_routing_table *rt,
> > > +			       struct kvm_kernel_irq_routing_entry *e,
> > >  			       const struct kvm_irq_routing_entry *ue)
> > >  {
> > >  	int r = -EINVAL;
> > > @@ -303,6 +300,7 @@ static int setup_routing_entry(struct kvm_kernel_irq_routing_entry *e,
> > >  		}
> > >  		e->irqchip.irqchip = ue->u.irqchip.irqchip;
> > >  		e->irqchip.pin = ue->u.irqchip.pin + delta;
> > > +		rt->chip[ue->u.irqchip.irqchip][e->irqchip.pin] = ue->gsi;
> > >  		break;
> > >  	case KVM_IRQ_ROUTING_MSI:
> > >  		e->set = kvm_set_msi;
> > > @@ -313,6 +311,8 @@ static int setup_routing_entry(struct kvm_kernel_irq_routing_entry *e,
> > >  	default:
> > >  		goto out;
> > >  	}
> > > +
> > > +	hlist_add_head(&e->link, &rt->map[e->gsi]);
> > >  	r = 0;
> > >  out:
> > >  	return r;
> > > @@ -324,23 +324,37 @@ int kvm_set_irq_routing(struct kvm *kvm,
> > >  			unsigned nr,
> > >  			unsigned flags)
> > >  {
> > > -	struct kvm_kernel_irq_routing_entry *new, *old;
> > > -	unsigned i;
> > > +	struct kvm_irq_routing_table *new, *old;
> > > +	u32 i, j, max_gsi = 0;
> > >  	int r;
> > >  
> > > -	/* last elemet is left zeored and indicates the end of the array */
> > > -	new = kzalloc(sizeof(*new) * (nr + 1), GFP_KERNEL);
> > > +	for (i = 0; i < nr; ++i) {
> > > +		if (ue[i].gsi >= KVM_MAX_IRQ_ROUTES)
> > > +			return -EINVAL;
> > > +		max_gsi = max(max_gsi, ue[i].gsi);
> > > +	}
> > > +
> > > +	max_gsi += 1;
> > > +
> > > +	new = kzalloc(sizeof(*new) + (max_gsi * sizeof(struct hlist_head)) +
> > > +		      (nr * sizeof(struct kvm_kernel_irq_routing_entry)),
> > > +		      GFP_KERNEL);
> > 
> > Why don't you allocate the hlist_head's and the routing entries
> > separately?
> > 
> I prefer it that way because cleanup after error is much easier. What
> are the disadvantages?

They are two data structures (two different arrays). Also as mentioned
before by others the allocation size of irq_routing array might become
an issue.

> > >  
> > >  	if (!new)
> > >  		return -ENOMEM;
> > >  
> > > +	new->rt_entries = (void *)&new->map[max_gsi];
> > > +
> > > +	new->max_gsi = max_gsi;
> > > +	for (i = 0; i < 3; i++)
> > > +		for (j = 0; j < KVM_IOAPIC_NUM_PINS; j++)
> > > +			new->chip[i][j] = -1;
> > > +
> > 
> > Should use something else instead of 3. Maybe dynamic for multiple
> > IOAPIC's support (but you can argue thats another problem).
> > 
> This is (another problem). The code has 1 IOAPIC hardcoded pretty deeply
> even at user/kernel API level. We will solve is some day.

OK
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