Re: [PATCH 1/4] Move irq routing data structure to rcu locking

[Gleb Natapov <gleb@redhat.com>]

On Mon, Jul 13, 2009 at 09:16:47AM -0400, Gregory Haskins wrote:
> Gleb Natapov wrote:
> > On Mon, Jul 13, 2009 at 09:01:33AM -0400, Gregory Haskins wrote:
> >   
> >> Gleb Natapov wrote:
> >>     
> >>> Signed-off-by: Gleb Natapov <gleb@redhat.com>
> >>> ---
> >>>  include/linux/kvm_host.h |    2 +-
> >>>  virt/kvm/irq_comm.c      |   55 +++++++++++++++++++++-------------------------
> >>>  virt/kvm/kvm_main.c      |    1 -
> >>>  3 files changed, 26 insertions(+), 32 deletions(-)
> >>>
> >>> diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h
> >>> index f54a0d3..6756b3e 100644
> >>> --- a/include/linux/kvm_host.h
> >>> +++ b/include/linux/kvm_host.h
> >>> @@ -161,7 +161,7 @@ struct kvm {
> >>>  
> >>>  	struct mutex irq_lock;
> >>>  #ifdef CONFIG_HAVE_KVM_IRQCHIP
> >>> -	struct list_head irq_routing; /* of kvm_kernel_irq_routing_entry */
> >>> +	struct kvm_kernel_irq_routing_entry *irq_routing;
> >>>  	struct hlist_head mask_notifier_list;
> >>>  #endif
> >>>  
> >>> diff --git a/virt/kvm/irq_comm.c b/virt/kvm/irq_comm.c
> >>> index 7af18b8..b2fa3f6 100644
> >>> --- a/virt/kvm/irq_comm.c
> >>> +++ b/virt/kvm/irq_comm.c
> >>> @@ -148,7 +148,8 @@ int kvm_set_irq(struct kvm *kvm, int irq_source_id, int irq, int level)
> >>>  	 * IOAPIC.  So set the bit in both. The guest will ignore
> >>>  	 * writes to the unused one.
> >>>  	 */
> >>> -	list_for_each_entry(e, &kvm->irq_routing, link)
> >>> +	rcu_read_lock();
> >>> +	for (e = rcu_dereference(kvm->irq_routing); e && e->set; e++) {
> >>>   
> >>>       
> >> Hi Gleb,
> >>   I haven't had a chance to fully digest and review these patches, but
> >> one thing I did notice is that you seem to be converting from a list to
> >> an open-coded structure.  I am just curious why you made this design
> >> decision instead of using the RCU variant of list?
> >>
> >>     
> > It is not scary "open-coded structure" it's just an array :) As I responded
> > to Michael the idea is to move msis out of irq_routing, make the array
> > much smaller and either use gsi as an index in the array or use hash table
> > instead looping over all entries. For now I can justify array as more
> > cache friendly data structure as we scan it linearly.
> >   
> 
> Ok, but that might be a good thing to mention in the patch header ;)
> 
What exactly?  Besides this is just an RFC. By the time it will be
applied (if at all) I may do the change already :)

> Kind Regards,
> -Greg
> 
> >   
> >> Regards,
> >> -Greg
> >>
> >>     
> >>>  		if (e->gsi == irq) {
> >>>  			int r = e->set(e, kvm, sig_level);
> >>>  			if (r < 0)
> >>> @@ -156,6 +157,8 @@ int kvm_set_irq(struct kvm *kvm, int irq_source_id, int irq, int level)
> >>>  
> >>>  			ret = r + ((ret < 0) ? 0 : ret);
> >>>  		}
> >>> +	}
> >>> +	rcu_read_unlock();
> >>>  	return ret;
> >>>  }
> >>>  
> >>> @@ -168,12 +171,15 @@ void kvm_notify_acked_irq(struct kvm *kvm, unsigned irqchip, unsigned pin)
> >>>  
> >>>  	trace_kvm_ack_irq(irqchip, pin);
> >>>  
> >>> -	list_for_each_entry(e, &kvm->irq_routing, link)
> >>> +	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;
> >>>  		}
> >>> +	}
> >>> +	rcu_read_unlock();
> >>>  
> >>>  	hlist_for_each_entry(kian, n, &kvm->arch.irq_ack_notifier_list, link)
> >>>  		if (kian->gsi == gsi)
> >>> @@ -264,19 +270,11 @@ void kvm_fire_mask_notifiers(struct kvm *kvm, int irq, bool mask)
> >>>  			kimn->func(kimn, mask);
> >>>  }
> >>>  
> >>> -static void __kvm_free_irq_routing(struct list_head *irq_routing)
> >>> -{
> >>> -	struct kvm_kernel_irq_routing_entry *e, *n;
> >>> -
> >>> -	list_for_each_entry_safe(e, n, irq_routing, link)
> >>> -		kfree(e);
> >>> -}
> >>> -
> >>>  void kvm_free_irq_routing(struct kvm *kvm)
> >>>  {
> >>> -	mutex_lock(&kvm->irq_lock);
> >>> -	__kvm_free_irq_routing(&kvm->irq_routing);
> >>> -	mutex_unlock(&kvm->irq_lock);
> >>> +	/* Called only during vm destruction. Nobody can use the pointer
> >>> +	   at this stage */
> >>> +	kfree(kvm->irq_routing);
> >>>  }
> >>>  
> >>>  static int setup_routing_entry(struct kvm_kernel_irq_routing_entry *e,
> >>> @@ -326,43 +324,40 @@ int kvm_set_irq_routing(struct kvm *kvm,
> >>>  			unsigned nr,
> >>>  			unsigned flags)
> >>>  {
> >>> -	struct list_head irq_list = LIST_HEAD_INIT(irq_list);
> >>> -	struct list_head tmp = LIST_HEAD_INIT(tmp);
> >>> -	struct kvm_kernel_irq_routing_entry *e = NULL;
> >>> +	struct kvm_kernel_irq_routing_entry *new, *old;
> >>>  	unsigned i;
> >>>  	int r;
> >>>  
> >>> +	/* last element is left zeroed and indicates the end of the array */
> >>> +	new = kzalloc(sizeof(*new) * (nr + 1), GFP_KERNEL);
> >>> +
> >>> +	if (!new)
> >>> +		return -ENOMEM;
> >>> +
> >>>  	for (i = 0; i < nr; ++i) {
> >>>  		r = -EINVAL;
> >>>  		if (ue->gsi >= KVM_MAX_IRQ_ROUTES)
> >>>  			goto out;
> >>>  		if (ue->flags)
> >>>  			goto out;
> >>> -		r = -ENOMEM;
> >>> -		e = kzalloc(sizeof(*e), GFP_KERNEL);
> >>> -		if (!e)
> >>> -			goto out;
> >>> -		r = setup_routing_entry(e, ue);
> >>> +		r = setup_routing_entry(new + i, ue);
> >>>  		if (r)
> >>>  			goto out;
> >>>  		++ue;
> >>> -		list_add(&e->link, &irq_list);
> >>> -		e = NULL;
> >>>  	}
> >>>  
> >>>  	mutex_lock(&kvm->irq_lock);
> >>> -	list_splice(&kvm->irq_routing, &tmp);
> >>> -	INIT_LIST_HEAD(&kvm->irq_routing);
> >>> -	list_splice(&irq_list, &kvm->irq_routing);
> >>> -	INIT_LIST_HEAD(&irq_list);
> >>> -	list_splice(&tmp, &irq_list);
> >>> +	old = kvm->irq_routing;
> >>> +	rcu_assign_pointer(kvm->irq_routing, new);
> >>>  	mutex_unlock(&kvm->irq_lock);
> >>>  
> >>> +	synchronize_rcu();
> >>> +
> >>>  	r = 0;
> >>> +	new = old;
> >>>  
> >>>  out:
> >>> -	kfree(e);
> >>> -	__kvm_free_irq_routing(&irq_list);
> >>> +	kfree(new);
> >>>  	return r;
> >>>  }
> >>>  
> >>> diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
> >>> index cf20dc1..24013b4 100644
> >>> --- a/virt/kvm/kvm_main.c
> >>> +++ b/virt/kvm/kvm_main.c
> >>> @@ -945,7 +945,6 @@ static struct kvm *kvm_create_vm(void)
> >>>  	if (IS_ERR(kvm))
> >>>  		goto out;
> >>>  #ifdef CONFIG_HAVE_KVM_IRQCHIP
> >>> -	INIT_LIST_HEAD(&kvm->irq_routing);
> >>>  	INIT_HLIST_HEAD(&kvm->mask_notifier_list);
> >>>  #endif
> >>>  
> >>>   
> >>>       
> >>     
> >
> >
> >
> > --
> > 			Gleb.
> > --
> > To unsubscribe from this list: send the line "unsubscribe kvm" in
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> >   
> 
> 



--
			Gleb.