[PATCH RFC] kvm: deliver msix interrupts from irq handler

[PATCH RFC] kvm: deliver msix interrupts from irq handler

[Michael S. Tsirkin]

We can deliver certain interrupts, notably MSIX,
from atomic context.  Add a new API kvm_set_irq_inatomic,
that does exactly that, and use it to implement
an irq handler for msi.

This reduces the pressure on scheduler in case
where host and guest irq share a host cpu.

Signed-off-by: Michael S. Tsirkin <mst@redhat.com>

Untested.
Note: this is on top of my host irq patch.
Probably needs to be rebased to be independent
and split up to new API + usage.

---
 include/linux/kvm_host.h |    2 +
 virt/kvm/assigned-dev.c  |   31 +++++++++++++++++++++++++-
 virt/kvm/irq_comm.c      |   52 ++++++++++++++++++++++++++++++++++++++++++++++
 3 files changed, 83 insertions(+), 2 deletions(-)

diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h
index f0361bc..e2b89ea 100644
--- a/include/linux/kvm_host.h
+++ b/include/linux/kvm_host.h
@@ -548,6 +548,8 @@ void kvm_get_intr_delivery_bitmask(struct kvm_ioapic *ioapic,
 #endif
 int kvm_set_irq(struct kvm *kvm, int irq_source_id, u32 irq, int level,
 		int host_irq);
+int kvm_set_irq_inatomic(struct kvm *kvm, int irq_source_id, u32 irq, int level,
+			 int host_irq);
 int kvm_set_msi(struct kvm_kernel_irq_routing_entry *irq_entry, struct kvm *kvm,
 		int irq_source_id, int level, int host_irq);
 void kvm_notify_acked_irq(struct kvm *kvm, unsigned irqchip, unsigned pin);
diff --git a/virt/kvm/assigned-dev.c b/virt/kvm/assigned-dev.c
index cc4bb7a..73bb001 100644
--- a/virt/kvm/assigned-dev.c
+++ b/virt/kvm/assigned-dev.c
@@ -57,6 +57,14 @@ static int find_index_from_host_irq(struct kvm_assigned_dev_kernel
 	return index;
 }
 
+static irqreturn_t kvm_assigned_dev_msi(int irq, void *dev_id)
+{
+	int ret = kvm_set_irq_inatomic(assigned_dev->kvm,
+				       assigned_dev->irq_source_id,
+				       assigned_dev->guest_irq, 1, irq);
+	return unlikely(ret == -EWOULDBLOCK) ? IRQ_WAKE_THREAD : IRQ_HANDLED;
+}
+
 static irqreturn_t kvm_assigned_dev_thread(int irq, void *dev_id)
 {
 	struct kvm_assigned_dev_kernel *assigned_dev = dev_id;
@@ -75,6 +83,23 @@ static irqreturn_t kvm_assigned_dev_thread(int irq, void *dev_id)
 }
 
 #ifdef __KVM_HAVE_MSIX
+static irqreturn_t kvm_assigned_dev_msix(int irq, void *dev_id)
+{
+	struct kvm_assigned_dev_kernel *assigned_dev = dev_id;
+	int index = find_index_from_host_irq(assigned_dev, irq);
+	u32 vector;
+	int ret = 0;
+
+	if (index >= 0) {
+		vector = assigned_dev->guest_msix_entries[index].vector;
+		ret = kvm_set_irq_inatomic(assigned_dev->kvm,
+					   assigned_dev->irq_source_id,
+					   vector, 1, irq);
+	}
+
+	return unlikely(ret == -EWOULDBLOCK) ? IRQ_WAKE_THREAD : IRQ_HANDLED;
+}
+
 static irqreturn_t kvm_assigned_dev_thread_msix(int irq, void *dev_id)
 {
 	struct kvm_assigned_dev_kernel *assigned_dev = dev_id;
@@ -266,7 +291,8 @@ static int assigned_device_enable_host_msi(struct kvm *kvm,
 	}
 
 	dev->host_irq = dev->dev->irq;
-	if (request_threaded_irq(dev->host_irq, NULL, kvm_assigned_dev_thread,
+	if (request_threaded_irq(dev->host_irq, kvm_assigned_dev_msi,
+				 kvm_assigned_dev_thread,
 				 0, dev->irq_name, dev)) {
 		pci_disable_msi(dev->dev);
 		return -EIO;
@@ -293,7 +319,8 @@ static int assigned_device_enable_host_msix(struct kvm *kvm,
 
 	for (i = 0; i < dev->entries_nr; i++) {
 		r = request_threaded_irq(dev->host_msix_entries[i].vector,
-					 NULL, kvm_assigned_dev_thread_msix,
+					 kvm_assigned_dev_msix,
+					 kvm_assigned_dev_thread_msix,
 					 0, dev->irq_name, dev);
 		if (r)
 			goto err;
diff --git a/virt/kvm/irq_comm.c b/virt/kvm/irq_comm.c
index ba892df..68cd127 100644
--- a/virt/kvm/irq_comm.c
+++ b/virt/kvm/irq_comm.c
@@ -201,6 +201,58 @@ int kvm_set_irq(struct kvm *kvm, int irq_source_id, u32 irq, int level,
 	return ret;
 }
 
+static inline struct kvm_kernel_irq_routing_entry *
+kvm_get_entry(struct kvm *kvm, struct kvm_irq_routing_table *irq_rq, u32 irq)
+{
+	struct kvm_kernel_irq_routing_entry *e;
+	if (likely(irq < irq_rt->nr_rt_entries))
+		hlist_for_each_entry(e, n, &irq_rt->map[irq], link)
+			if (e->type == KVM_IRQ_ROUTING_MSI)
+				return e;
+			else
+				return ERR_PTR(-EWOULDBLOCK);
+	return ERR_PTR(-EINVAL);
+}
+
+/*
+ * Deliver an IRQ in an atomic context if we can, or return a failure,
+ * user can retry in a process context.
+ * Return value:
+ *  -EWOULDBLOCK	Can't deliver in atomic context
+ *  < 0			Interrupt was ignored (masked or not delivered for other reasons)
+ *  = 0			Interrupt was coalesced (previous irq is still pending)
+ *  > 0			Number of CPUs interrupt was delivered to
+ */
+int kvm_set_irq_inatomic(struct kvm *kvm, int irq_source_id, u32 irq, int level,
+			 int host_irq)
+{
+	struct kvm_kernel_irq_routing_entry *e;
+	int ret = -EINVAL;
+	struct kvm_irq_routing_table *irq_rt;
+	struct hlist_node *n;
+
+	trace_kvm_set_irq(irq, level, irq_source_id);
+
+	/*
+	 * We know MSI are safe in interrupt context. They are also
+	 * easy as there's a single routing entry for these GSIs.
+	 * So only handle MSI in an atomic context, for now.
+	 */
+	rcu_read_lock_bh();
+	irq_rt = rcu_dereference(kvm->irq_routing);
+	if (irq < irq_rt->nr_rt_entries)
+		hlist_for_each_entry(e, n, &irq_rt->map[irq], link) {
+			if (ei->type == KVM_IRQ_ROUTING_MSI)
+				ret = kvm_set_msi(e, kvm, irq_source_id, level,
+						  host_irq);
+			else
+				ret = -EWOULDBLOCK;
+			break;
+		}
+	rcu_read_unlock_bh();
+	return ret;
+}
+
 void kvm_notify_acked_irq(struct kvm *kvm, unsigned irqchip, unsigned pin)
 {
 	struct kvm_irq_ack_notifier *kian;
-- 
1.7.8.2.325.g247f9

Re: [PATCH RFC] kvm: deliver msix interrupts from irq handler

[Gleb Natapov]

On Wed, Jan 18, 2012 at 08:10:24PM +0200, Michael S. Tsirkin wrote:
> We can deliver certain interrupts, notably MSIX,
> from atomic context.  Add a new API kvm_set_irq_inatomic,
> that does exactly that, and use it to implement
> an irq handler for msi.
> 
> This reduces the pressure on scheduler in case
> where host and guest irq share a host cpu.
> 
> Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
> 
> Untested.
> Note: this is on top of my host irq patch.
> Probably needs to be rebased to be independent
> and split up to new API + usage.
> 
> ---
>  include/linux/kvm_host.h |    2 +
>  virt/kvm/assigned-dev.c  |   31 +++++++++++++++++++++++++-
>  virt/kvm/irq_comm.c      |   52 ++++++++++++++++++++++++++++++++++++++++++++++
>  3 files changed, 83 insertions(+), 2 deletions(-)
> 
> diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h
> index f0361bc..e2b89ea 100644
> --- a/include/linux/kvm_host.h
> +++ b/include/linux/kvm_host.h
> @@ -548,6 +548,8 @@ void kvm_get_intr_delivery_bitmask(struct kvm_ioapic *ioapic,
>  #endif
>  int kvm_set_irq(struct kvm *kvm, int irq_source_id, u32 irq, int level,
>  		int host_irq);
> +int kvm_set_irq_inatomic(struct kvm *kvm, int irq_source_id, u32 irq, int level,
> +			 int host_irq);
>  int kvm_set_msi(struct kvm_kernel_irq_routing_entry *irq_entry, struct kvm *kvm,
>  		int irq_source_id, int level, int host_irq);
>  void kvm_notify_acked_irq(struct kvm *kvm, unsigned irqchip, unsigned pin);
> diff --git a/virt/kvm/assigned-dev.c b/virt/kvm/assigned-dev.c
> index cc4bb7a..73bb001 100644
> --- a/virt/kvm/assigned-dev.c
> +++ b/virt/kvm/assigned-dev.c
> @@ -57,6 +57,14 @@ static int find_index_from_host_irq(struct kvm_assigned_dev_kernel
>  	return index;
>  }
>  
> +static irqreturn_t kvm_assigned_dev_msi(int irq, void *dev_id)
> +{
> +	int ret = kvm_set_irq_inatomic(assigned_dev->kvm,
> +				       assigned_dev->irq_source_id,
> +				       assigned_dev->guest_irq, 1, irq);
> +	return unlikely(ret == -EWOULDBLOCK) ? IRQ_WAKE_THREAD : IRQ_HANDLED;
> +}
> +
>  static irqreturn_t kvm_assigned_dev_thread(int irq, void *dev_id)
>  {
>  	struct kvm_assigned_dev_kernel *assigned_dev = dev_id;
> @@ -75,6 +83,23 @@ static irqreturn_t kvm_assigned_dev_thread(int irq, void *dev_id)
>  }
>  
>  #ifdef __KVM_HAVE_MSIX
> +static irqreturn_t kvm_assigned_dev_msix(int irq, void *dev_id)
> +{
> +	struct kvm_assigned_dev_kernel *assigned_dev = dev_id;
> +	int index = find_index_from_host_irq(assigned_dev, irq);
> +	u32 vector;
> +	int ret = 0;
> +
> +	if (index >= 0) {
> +		vector = assigned_dev->guest_msix_entries[index].vector;
> +		ret = kvm_set_irq_inatomic(assigned_dev->kvm,
> +					   assigned_dev->irq_source_id,
> +					   vector, 1, irq);
> +	}
> +
> +	return unlikely(ret == -EWOULDBLOCK) ? IRQ_WAKE_THREAD : IRQ_HANDLED;
> +}
> +
>  static irqreturn_t kvm_assigned_dev_thread_msix(int irq, void *dev_id)
>  {
>  	struct kvm_assigned_dev_kernel *assigned_dev = dev_id;
> @@ -266,7 +291,8 @@ static int assigned_device_enable_host_msi(struct kvm *kvm,
>  	}
>  
>  	dev->host_irq = dev->dev->irq;
> -	if (request_threaded_irq(dev->host_irq, NULL, kvm_assigned_dev_thread,
> +	if (request_threaded_irq(dev->host_irq, kvm_assigned_dev_msi,
> +				 kvm_assigned_dev_thread,
>  				 0, dev->irq_name, dev)) {
>  		pci_disable_msi(dev->dev);
>  		return -EIO;
> @@ -293,7 +319,8 @@ static int assigned_device_enable_host_msix(struct kvm *kvm,
>  
>  	for (i = 0; i < dev->entries_nr; i++) {
>  		r = request_threaded_irq(dev->host_msix_entries[i].vector,
> -					 NULL, kvm_assigned_dev_thread_msix,
> +					 kvm_assigned_dev_msix,
> +					 kvm_assigned_dev_thread_msix,
>  					 0, dev->irq_name, dev);
>  		if (r)
>  			goto err;
> diff --git a/virt/kvm/irq_comm.c b/virt/kvm/irq_comm.c
> index ba892df..68cd127 100644
> --- a/virt/kvm/irq_comm.c
> +++ b/virt/kvm/irq_comm.c
> @@ -201,6 +201,58 @@ int kvm_set_irq(struct kvm *kvm, int irq_source_id, u32 irq, int level,
>  	return ret;
>  }
>  
> +static inline struct kvm_kernel_irq_routing_entry *
> +kvm_get_entry(struct kvm *kvm, struct kvm_irq_routing_table *irq_rq, u32 irq)
> +{
> +	struct kvm_kernel_irq_routing_entry *e;
> +	if (likely(irq < irq_rt->nr_rt_entries))
> +		hlist_for_each_entry(e, n, &irq_rt->map[irq], link)
> +			if (e->type == KVM_IRQ_ROUTING_MSI)
> +				return e;
> +			else
> +				return ERR_PTR(-EWOULDBLOCK);
> +	return ERR_PTR(-EINVAL);
> +}
Unused?

> +
> +/*
> + * Deliver an IRQ in an atomic context if we can, or return a failure,
> + * user can retry in a process context.
> + * Return value:
> + *  -EWOULDBLOCK	Can't deliver in atomic context
> + *  < 0			Interrupt was ignored (masked or not delivered for other reasons)
> + *  = 0			Interrupt was coalesced (previous irq is still pending)
> + *  > 0			Number of CPUs interrupt was delivered to
> + */
> +int kvm_set_irq_inatomic(struct kvm *kvm, int irq_source_id, u32 irq, int level,
> +			 int host_irq)
> +{
> +	struct kvm_kernel_irq_routing_entry *e;
> +	int ret = -EINVAL;
> +	struct kvm_irq_routing_table *irq_rt;
> +	struct hlist_node *n;
> +
> +	trace_kvm_set_irq(irq, level, irq_source_id);
> +
> +	/*
> +	 * We know MSI are safe in interrupt context. They are also
> +	 * easy as there's a single routing entry for these GSIs.
> +	 * So only handle MSI in an atomic context, for now.
> +	 */
> +	rcu_read_lock_bh();
_bh?

/**
 * rcu_read_lock_bh() - mark the beginning of an RCU-bh critical section
 *
 * This is equivalent of rcu_read_lock(), but to be used when updates
 * are being done using call_rcu_bh() or synchronize_rcu_bh().
 ....

Since updates to irq routing table are not done using _bh variant I
doubt rcu_read_lock_bh() is justified here.

> +	irq_rt = rcu_dereference(kvm->irq_routing);
> +	if (irq < irq_rt->nr_rt_entries)
> +		hlist_for_each_entry(e, n, &irq_rt->map[irq], link) {
> +			if (ei->type == KVM_IRQ_ROUTING_MSI)
> +				ret = kvm_set_msi(e, kvm, irq_source_id, level,
> +						  host_irq);
> +			else
> +				ret = -EWOULDBLOCK;
> +			break;
> +		}
> +	rcu_read_unlock_bh();
> +	return ret;
> +}
> +
Share implementation with kvm_set_irq().

>  void kvm_notify_acked_irq(struct kvm *kvm, unsigned irqchip, unsigned pin)
>  {
>  	struct kvm_irq_ack_notifier *kian;
> -- 
> 1.7.8.2.325.g247f9
> --
> To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
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--
			Gleb.

Re: [PATCH RFC] kvm: deliver msix interrupts from irq handler

[Jan Kiszka]

On 2012-01-18 19:10, Michael S. Tsirkin wrote:
> We can deliver certain interrupts, notably MSIX,
> from atomic context.  Add a new API kvm_set_irq_inatomic,
> that does exactly that, and use it to implement
> an irq handler for msi.
> 
> This reduces the pressure on scheduler in case
> where host and guest irq share a host cpu.
> 
> Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
> 
> Untested.
> Note: this is on top of my host irq patch.
> Probably needs to be rebased to be independent
> and split up to new API + usage.
> 
> ---
>  include/linux/kvm_host.h |    2 +
>  virt/kvm/assigned-dev.c  |   31 +++++++++++++++++++++++++-
>  virt/kvm/irq_comm.c      |   52 ++++++++++++++++++++++++++++++++++++++++++++++
>  3 files changed, 83 insertions(+), 2 deletions(-)
> 
> diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h
> index f0361bc..e2b89ea 100644
> --- a/include/linux/kvm_host.h
> +++ b/include/linux/kvm_host.h
> @@ -548,6 +548,8 @@ void kvm_get_intr_delivery_bitmask(struct kvm_ioapic *ioapic,
>  #endif
>  int kvm_set_irq(struct kvm *kvm, int irq_source_id, u32 irq, int level,
>  		int host_irq);
> +int kvm_set_irq_inatomic(struct kvm *kvm, int irq_source_id, u32 irq, int level,
> +			 int host_irq);
>  int kvm_set_msi(struct kvm_kernel_irq_routing_entry *irq_entry, struct kvm *kvm,
>  		int irq_source_id, int level, int host_irq);
>  void kvm_notify_acked_irq(struct kvm *kvm, unsigned irqchip, unsigned pin);
> diff --git a/virt/kvm/assigned-dev.c b/virt/kvm/assigned-dev.c
> index cc4bb7a..73bb001 100644
> --- a/virt/kvm/assigned-dev.c
> +++ b/virt/kvm/assigned-dev.c
> @@ -57,6 +57,14 @@ static int find_index_from_host_irq(struct kvm_assigned_dev_kernel
>  	return index;
>  }
>  
> +static irqreturn_t kvm_assigned_dev_msi(int irq, void *dev_id)
> +{
> +	int ret = kvm_set_irq_inatomic(assigned_dev->kvm,
> +				       assigned_dev->irq_source_id,
> +				       assigned_dev->guest_irq, 1, irq);
> +	return unlikely(ret == -EWOULDBLOCK) ? IRQ_WAKE_THREAD : IRQ_HANDLED;
> +}

This function gets unused (in theory) if !__KVM_HAVE_MSIX &&
!__KVM_HAVE_MSI. Should be fixed for consistency reasons.

> +
>  static irqreturn_t kvm_assigned_dev_thread(int irq, void *dev_id)
>  {
>  	struct kvm_assigned_dev_kernel *assigned_dev = dev_id;
> @@ -75,6 +83,23 @@ static irqreturn_t kvm_assigned_dev_thread(int irq, void *dev_id)
>  }
>  
>  #ifdef __KVM_HAVE_MSIX
> +static irqreturn_t kvm_assigned_dev_msix(int irq, void *dev_id)
> +{
> +	struct kvm_assigned_dev_kernel *assigned_dev = dev_id;
> +	int index = find_index_from_host_irq(assigned_dev, irq);
> +	u32 vector;
> +	int ret = 0;
> +
> +	if (index >= 0) {
> +		vector = assigned_dev->guest_msix_entries[index].vector;
> +		ret = kvm_set_irq_inatomic(assigned_dev->kvm,
> +					   assigned_dev->irq_source_id,
> +					   vector, 1, irq);
> +	}
> +
> +	return unlikely(ret == -EWOULDBLOCK) ? IRQ_WAKE_THREAD : IRQ_HANDLED;
> +}
> +
>  static irqreturn_t kvm_assigned_dev_thread_msix(int irq, void *dev_id)
>  {
>  	struct kvm_assigned_dev_kernel *assigned_dev = dev_id;
> @@ -266,7 +291,8 @@ static int assigned_device_enable_host_msi(struct kvm *kvm,
>  	}
>  
>  	dev->host_irq = dev->dev->irq;
> -	if (request_threaded_irq(dev->host_irq, NULL, kvm_assigned_dev_thread,
> +	if (request_threaded_irq(dev->host_irq, kvm_assigned_dev_msi,
> +				 kvm_assigned_dev_thread,
>  				 0, dev->irq_name, dev)) {
>  		pci_disable_msi(dev->dev);
>  		return -EIO;
> @@ -293,7 +319,8 @@ static int assigned_device_enable_host_msix(struct kvm *kvm,
>  
>  	for (i = 0; i < dev->entries_nr; i++) {
>  		r = request_threaded_irq(dev->host_msix_entries[i].vector,
> -					 NULL, kvm_assigned_dev_thread_msix,
> +					 kvm_assigned_dev_msix,
> +					 kvm_assigned_dev_thread_msix,
>  					 0, dev->irq_name, dev);
>  		if (r)
>  			goto err;
> diff --git a/virt/kvm/irq_comm.c b/virt/kvm/irq_comm.c
> index ba892df..68cd127 100644
> --- a/virt/kvm/irq_comm.c
> +++ b/virt/kvm/irq_comm.c
> @@ -201,6 +201,58 @@ int kvm_set_irq(struct kvm *kvm, int irq_source_id, u32 irq, int level,
>  	return ret;
>  }
>  
> +static inline struct kvm_kernel_irq_routing_entry *
> +kvm_get_entry(struct kvm *kvm, struct kvm_irq_routing_table *irq_rq, u32 irq)
> +{
> +	struct kvm_kernel_irq_routing_entry *e;
> +	if (likely(irq < irq_rt->nr_rt_entries))
> +		hlist_for_each_entry(e, n, &irq_rt->map[irq], link)
> +			if (e->type == KVM_IRQ_ROUTING_MSI)
> +				return e;
> +			else
> +				return ERR_PTR(-EWOULDBLOCK);
> +	return ERR_PTR(-EINVAL);
> +}
> +
> +/*
> + * Deliver an IRQ in an atomic context if we can, or return a failure,
> + * user can retry in a process context.
> + * Return value:
> + *  -EWOULDBLOCK	Can't deliver in atomic context
> + *  < 0			Interrupt was ignored (masked or not delivered for other reasons)
> + *  = 0			Interrupt was coalesced (previous irq is still pending)
> + *  > 0			Number of CPUs interrupt was delivered to

Where do you make use of =0 vs. >0? Not in this patch at least. Do you
consider using it for the APIC timer as well?

> + */
> +int kvm_set_irq_inatomic(struct kvm *kvm, int irq_source_id, u32 irq, int level,
> +			 int host_irq)
> +{
> +	struct kvm_kernel_irq_routing_entry *e;
> +	int ret = -EINVAL;
> +	struct kvm_irq_routing_table *irq_rt;
> +	struct hlist_node *n;
> +
> +	trace_kvm_set_irq(irq, level, irq_source_id);
> +
> +	/*
> +	 * We know MSI are safe in interrupt context. They are also
> +	 * easy as there's a single routing entry for these GSIs.
> +	 * So only handle MSI in an atomic context, for now.
> +	 */
> +	rcu_read_lock_bh();
> +	irq_rt = rcu_dereference(kvm->irq_routing);
> +	if (irq < irq_rt->nr_rt_entries)
> +		hlist_for_each_entry(e, n, &irq_rt->map[irq], link) {
> +			if (ei->type == KVM_IRQ_ROUTING_MSI)
> +				ret = kvm_set_msi(e, kvm, irq_source_id, level,
> +						  host_irq);
> +			else
> +				ret = -EWOULDBLOCK;
> +			break;
> +		}
> +	rcu_read_unlock_bh();
> +	return ret;
> +}
> +
>  void kvm_notify_acked_irq(struct kvm *kvm, unsigned irqchip, unsigned pin)
>  {
>  	struct kvm_irq_ack_notifier *kian;

Highly welcome feature!

Jan

-- 
Siemens AG, Corporate Technology, CT T DE IT 1
Corporate Competence Center Embedded Linux

Re: [PATCH RFC] kvm: deliver msix interrupts from irq handler

[Michael S. Tsirkin]

On Thu, Jan 19, 2012 at 09:21:23AM +0200, Gleb Natapov wrote:
> > diff --git a/virt/kvm/irq_comm.c b/virt/kvm/irq_comm.c
> > index ba892df..68cd127 100644
> > --- a/virt/kvm/irq_comm.c
> > +++ b/virt/kvm/irq_comm.c
> > @@ -201,6 +201,58 @@ int kvm_set_irq(struct kvm *kvm, int irq_source_id, u32 irq, int level,
> >  	return ret;
> >  }
> >  
> > +static inline struct kvm_kernel_irq_routing_entry *
> > +kvm_get_entry(struct kvm *kvm, struct kvm_irq_routing_table *irq_rq, u32 irq)
> > +{
> > +	struct kvm_kernel_irq_routing_entry *e;
> > +	if (likely(irq < irq_rt->nr_rt_entries))
> > +		hlist_for_each_entry(e, n, &irq_rt->map[irq], link)
> > +			if (e->type == KVM_IRQ_ROUTING_MSI)
> > +				return e;
> > +			else
> > +				return ERR_PTR(-EWOULDBLOCK);
> > +	return ERR_PTR(-EINVAL);
> > +}
> Unused?

Yes, leftovers from an attempt to reuse kvm_set_irq as you suggested
below. It didn't work out - we get much more code this way,
so this needs to be removed.

> > +
> > +/*
> > + * Deliver an IRQ in an atomic context if we can, or return a failure,
> > + * user can retry in a process context.
> > + * Return value:
> > + *  -EWOULDBLOCK	Can't deliver in atomic context
> > + *  < 0			Interrupt was ignored (masked or not delivered for other reasons)
> > + *  = 0			Interrupt was coalesced (previous irq is still pending)
> > + *  > 0			Number of CPUs interrupt was delivered to
> > + */
> > +int kvm_set_irq_inatomic(struct kvm *kvm, int irq_source_id, u32 irq, int level,
> > +			 int host_irq)
> > +{
> > +	struct kvm_kernel_irq_routing_entry *e;
> > +	int ret = -EINVAL;
> > +	struct kvm_irq_routing_table *irq_rt;
> > +	struct hlist_node *n;
> > +
> > +	trace_kvm_set_irq(irq, level, irq_source_id);
> > +
> > +	/*
> > +	 * We know MSI are safe in interrupt context. They are also
> > +	 * easy as there's a single routing entry for these GSIs.
> > +	 * So only handle MSI in an atomic context, for now.
> > +	 */
> > +	rcu_read_lock_bh();
> _bh?
> 
> /**
>  * rcu_read_lock_bh() - mark the beginning of an RCU-bh critical section
>  *
>  * This is equivalent of rcu_read_lock(), but to be used when updates
>  * are being done using call_rcu_bh() or synchronize_rcu_bh().
>  ....
> 
> Since updates to irq routing table are not done using _bh variant I
> doubt rcu_read_lock_bh() is justified here.

Right. Thanks for ppointing this out, I was confused.

> > +	irq_rt = rcu_dereference(kvm->irq_routing);
> > +	if (irq < irq_rt->nr_rt_entries)
> > +		hlist_for_each_entry(e, n, &irq_rt->map[irq], link) {
> > +			if (ei->type == KVM_IRQ_ROUTING_MSI)
> > +				ret = kvm_set_msi(e, kvm, irq_source_id, level,
> > +						  host_irq);
> > +			else
> > +				ret = -EWOULDBLOCK;
> > +			break;
> > +		}
> > +	rcu_read_unlock_bh();
> > +	return ret;
> > +}
> > +
> Share implementation with kvm_set_irq().

I considered this. There are several reasons not to do it:
- Amount of common code is very small
- As it's separate, it's more obvious that it can't block (kvm_set_irq can block)
  We can even tag kvm_set_irq with might_sleep.
- This is way simpler and faster as we can do operations directly,
  instead of copying the irq out, and as it's datapath
  an optimization is I think justified.

> >  void kvm_notify_acked_irq(struct kvm *kvm, unsigned irqchip, unsigned pin)
> >  {
> >  	struct kvm_irq_ack_notifier *kian;
> > -- 
> > 1.7.8.2.325.g247f9
> > --
> > To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
> > the body of a message to majordomo@vger.kernel.org
> > More majordomo info at  http://vger.kernel.org/majordomo-info.html
> > Please read the FAQ at  http://www.tux.org/lkml/
> 
> --
> 			Gleb.

Re: [PATCH RFC] kvm: deliver msix interrupts from irq handler

[Michael S. Tsirkin]

On Thu, Jan 19, 2012 at 01:04:32PM +0100, Jan Kiszka wrote:
> On 2012-01-18 19:10, Michael S. Tsirkin wrote:
> > We can deliver certain interrupts, notably MSIX,
> > from atomic context.  Add a new API kvm_set_irq_inatomic,
> > that does exactly that, and use it to implement
> > an irq handler for msi.
> > 
> > This reduces the pressure on scheduler in case
> > where host and guest irq share a host cpu.
> > 
> > Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
> > 
> > Untested.
> > Note: this is on top of my host irq patch.
> > Probably needs to be rebased to be independent
> > and split up to new API + usage.
> > 
> > ---
> >  include/linux/kvm_host.h |    2 +
> >  virt/kvm/assigned-dev.c  |   31 +++++++++++++++++++++++++-
> >  virt/kvm/irq_comm.c      |   52 ++++++++++++++++++++++++++++++++++++++++++++++
> >  3 files changed, 83 insertions(+), 2 deletions(-)
> > 
> > diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h
> > index f0361bc..e2b89ea 100644
> > --- a/include/linux/kvm_host.h
> > +++ b/include/linux/kvm_host.h
> > @@ -548,6 +548,8 @@ void kvm_get_intr_delivery_bitmask(struct kvm_ioapic *ioapic,
> >  #endif
> >  int kvm_set_irq(struct kvm *kvm, int irq_source_id, u32 irq, int level,
> >  		int host_irq);
> > +int kvm_set_irq_inatomic(struct kvm *kvm, int irq_source_id, u32 irq, int level,
> > +			 int host_irq);
> >  int kvm_set_msi(struct kvm_kernel_irq_routing_entry *irq_entry, struct kvm *kvm,
> >  		int irq_source_id, int level, int host_irq);
> >  void kvm_notify_acked_irq(struct kvm *kvm, unsigned irqchip, unsigned pin);
> > diff --git a/virt/kvm/assigned-dev.c b/virt/kvm/assigned-dev.c
> > index cc4bb7a..73bb001 100644
> > --- a/virt/kvm/assigned-dev.c
> > +++ b/virt/kvm/assigned-dev.c
> > @@ -57,6 +57,14 @@ static int find_index_from_host_irq(struct kvm_assigned_dev_kernel
> >  	return index;
> >  }
> >  
> > +static irqreturn_t kvm_assigned_dev_msi(int irq, void *dev_id)
> > +{
> > +	int ret = kvm_set_irq_inatomic(assigned_dev->kvm,
> > +				       assigned_dev->irq_source_id,
> > +				       assigned_dev->guest_irq, 1, irq);
> > +	return unlikely(ret == -EWOULDBLOCK) ? IRQ_WAKE_THREAD : IRQ_HANDLED;
> > +}
> 
> This function gets unused (in theory) if !__KVM_HAVE_MSIX &&
> !__KVM_HAVE_MSI. Should be fixed for consistency reasons.

Does kvm still build with this !__KVM_HAVE_MSI? It does not look like
it would ...


> > +
> >  static irqreturn_t kvm_assigned_dev_thread(int irq, void *dev_id)
> >  {
> >  	struct kvm_assigned_dev_kernel *assigned_dev = dev_id;
> > @@ -75,6 +83,23 @@ static irqreturn_t kvm_assigned_dev_thread(int irq, void *dev_id)
> >  }
> >  
> >  #ifdef __KVM_HAVE_MSIX
> > +static irqreturn_t kvm_assigned_dev_msix(int irq, void *dev_id)
> > +{
> > +	struct kvm_assigned_dev_kernel *assigned_dev = dev_id;
> > +	int index = find_index_from_host_irq(assigned_dev, irq);
> > +	u32 vector;
> > +	int ret = 0;
> > +
> > +	if (index >= 0) {
> > +		vector = assigned_dev->guest_msix_entries[index].vector;
> > +		ret = kvm_set_irq_inatomic(assigned_dev->kvm,
> > +					   assigned_dev->irq_source_id,
> > +					   vector, 1, irq);
> > +	}
> > +
> > +	return unlikely(ret == -EWOULDBLOCK) ? IRQ_WAKE_THREAD : IRQ_HANDLED;
> > +}
> > +
> >  static irqreturn_t kvm_assigned_dev_thread_msix(int irq, void *dev_id)
> >  {
> >  	struct kvm_assigned_dev_kernel *assigned_dev = dev_id;
> > @@ -266,7 +291,8 @@ static int assigned_device_enable_host_msi(struct kvm *kvm,
> >  	}
> >  
> >  	dev->host_irq = dev->dev->irq;
> > -	if (request_threaded_irq(dev->host_irq, NULL, kvm_assigned_dev_thread,
> > +	if (request_threaded_irq(dev->host_irq, kvm_assigned_dev_msi,
> > +				 kvm_assigned_dev_thread,
> >  				 0, dev->irq_name, dev)) {
> >  		pci_disable_msi(dev->dev);
> >  		return -EIO;
> > @@ -293,7 +319,8 @@ static int assigned_device_enable_host_msix(struct kvm *kvm,
> >  
> >  	for (i = 0; i < dev->entries_nr; i++) {
> >  		r = request_threaded_irq(dev->host_msix_entries[i].vector,
> > -					 NULL, kvm_assigned_dev_thread_msix,
> > +					 kvm_assigned_dev_msix,
> > +					 kvm_assigned_dev_thread_msix,
> >  					 0, dev->irq_name, dev);
> >  		if (r)
> >  			goto err;
> > diff --git a/virt/kvm/irq_comm.c b/virt/kvm/irq_comm.c
> > index ba892df..68cd127 100644
> > --- a/virt/kvm/irq_comm.c
> > +++ b/virt/kvm/irq_comm.c
> > @@ -201,6 +201,58 @@ int kvm_set_irq(struct kvm *kvm, int irq_source_id, u32 irq, int level,
> >  	return ret;
> >  }
> >  
> > +static inline struct kvm_kernel_irq_routing_entry *
> > +kvm_get_entry(struct kvm *kvm, struct kvm_irq_routing_table *irq_rq, u32 irq)
> > +{
> > +	struct kvm_kernel_irq_routing_entry *e;
> > +	if (likely(irq < irq_rt->nr_rt_entries))
> > +		hlist_for_each_entry(e, n, &irq_rt->map[irq], link)
> > +			if (e->type == KVM_IRQ_ROUTING_MSI)
> > +				return e;
> > +			else
> > +				return ERR_PTR(-EWOULDBLOCK);
> > +	return ERR_PTR(-EINVAL);
> > +}
> > +
> > +/*
> > + * Deliver an IRQ in an atomic context if we can, or return a failure,
> > + * user can retry in a process context.
> > + * Return value:
> > + *  -EWOULDBLOCK	Can't deliver in atomic context
> > + *  < 0			Interrupt was ignored (masked or not delivered for other reasons)
> > + *  = 0			Interrupt was coalesced (previous irq is still pending)
> > + *  > 0			Number of CPUs interrupt was delivered to
> 
> Where do you make use of =0 vs. >0? Not in this patch at least. Do you
> consider using it for the APIC timer as well?

I think it might be handy in the future. It's an internal function
(not exported) so I just return what I get without worrying about it
too much: I didn't need to add code to get this :)

> > + */
> > +int kvm_set_irq_inatomic(struct kvm *kvm, int irq_source_id, u32 irq, int level,
> > +			 int host_irq)
> > +{
> > +	struct kvm_kernel_irq_routing_entry *e;
> > +	int ret = -EINVAL;
> > +	struct kvm_irq_routing_table *irq_rt;
> > +	struct hlist_node *n;
> > +
> > +	trace_kvm_set_irq(irq, level, irq_source_id);
> > +
> > +	/*
> > +	 * We know MSI are safe in interrupt context. They are also
> > +	 * easy as there's a single routing entry for these GSIs.
> > +	 * So only handle MSI in an atomic context, for now.
> > +	 */
> > +	rcu_read_lock_bh();
> > +	irq_rt = rcu_dereference(kvm->irq_routing);
> > +	if (irq < irq_rt->nr_rt_entries)
> > +		hlist_for_each_entry(e, n, &irq_rt->map[irq], link) {
> > +			if (ei->type == KVM_IRQ_ROUTING_MSI)
> > +				ret = kvm_set_msi(e, kvm, irq_source_id, level,
> > +						  host_irq);
> > +			else
> > +				ret = -EWOULDBLOCK;
> > +			break;
> > +		}
> > +	rcu_read_unlock_bh();
> > +	return ret;
> > +}
> > +
> >  void kvm_notify_acked_irq(struct kvm *kvm, unsigned irqchip, unsigned pin)
> >  {
> >  	struct kvm_irq_ack_notifier *kian;
> 
> Highly welcome feature!
> 
> Jan

I think we need to fix MSIX masking now, otherwise delivering interrupt
faster might get us a storm of interrupts.

> -- 
> Siemens AG, Corporate Technology, CT T DE IT 1
> Corporate Competence Center Embedded Linux

Re: [PATCH RFC] kvm: deliver msix interrupts from irq handler

[Gleb Natapov]

On Thu, Jan 19, 2012 at 03:49:57PM +0200, Michael S. Tsirkin wrote:
> > > +	irq_rt = rcu_dereference(kvm->irq_routing);
> > > +	if (irq < irq_rt->nr_rt_entries)
> > > +		hlist_for_each_entry(e, n, &irq_rt->map[irq], link) {
> > > +			if (ei->type == KVM_IRQ_ROUTING_MSI)
> > > +				ret = kvm_set_msi(e, kvm, irq_source_id, level,
> > > +						  host_irq);
> > > +			else
> > > +				ret = -EWOULDBLOCK;
> > > +			break;
> > > +		}
> > > +	rcu_read_unlock_bh();
> > > +	return ret;
> > > +}
> > > +
> > Share implementation with kvm_set_irq().
> 
> I considered this. There are several reasons not to do it:
> - Amount of common code is very small
Why? Just pass msi_only flag to kvm_set_irq() and skip an entry if flag is
set and entry type is not msi.

> - As it's separate, it's more obvious that it can't block (kvm_set_irq can block)
>   We can even tag kvm_set_irq with might_sleep.
They can still be two separate function calling common one.

> - This is way simpler and faster as we can do operations directly,
>   instead of copying the irq out, and as it's datapath
>   an optimization is I think justified.
I really do not think the copy of one small data structure will be
measurable. If it is (has to be proven) we can optimize that two
in the common code.

--
			Gleb.

Re: [PATCH RFC] kvm: deliver msix interrupts from irq handler

[Michael S. Tsirkin]

On Thu, Jan 19, 2012 at 05:02:17PM +0200, Gleb Natapov wrote:
> On Thu, Jan 19, 2012 at 03:49:57PM +0200, Michael S. Tsirkin wrote:
> > > > +	irq_rt = rcu_dereference(kvm->irq_routing);
> > > > +	if (irq < irq_rt->nr_rt_entries)
> > > > +		hlist_for_each_entry(e, n, &irq_rt->map[irq], link) {
> > > > +			if (ei->type == KVM_IRQ_ROUTING_MSI)
> > > > +				ret = kvm_set_msi(e, kvm, irq_source_id, level,
> > > > +						  host_irq);
> > > > +			else
> > > > +				ret = -EWOULDBLOCK;
> > > > +			break;
> > > > +		}
> > > > +	rcu_read_unlock_bh();
> > > > +	return ret;
> > > > +}
> > > > +
> > > Share implementation with kvm_set_irq().
> > 
> > I considered this. There are several reasons not to do it:
> > - Amount of common code is very small
> Why? Just pass msi_only flag to kvm_set_irq() and skip an entry if flag is
> set and entry type is not msi.
> 
> > - As it's separate, it's more obvious that it can't block (kvm_set_irq can block)
> >   We can even tag kvm_set_irq with might_sleep.
> They can still be two separate function calling common one.

No, the common code is the surrounding foreach loop,
the internal if branch is different.

> > - This is way simpler and faster as we can do operations directly,
> >   instead of copying the irq out, and as it's datapath
> >   an optimization is I think justified.
> I really do not think the copy of one small data structure will be
> measurable. If it is (has to be proven) we can optimize that two
> in the common code.
> 
> --
> 			Gleb.

Re: [PATCH RFC] kvm: deliver msix interrupts from irq handler

[Gleb Natapov]

On Thu, Jan 19, 2012 at 05:57:48PM +0200, Michael S. Tsirkin wrote:
> On Thu, Jan 19, 2012 at 05:02:17PM +0200, Gleb Natapov wrote:
> > On Thu, Jan 19, 2012 at 03:49:57PM +0200, Michael S. Tsirkin wrote:
> > > > > +	irq_rt = rcu_dereference(kvm->irq_routing);
> > > > > +	if (irq < irq_rt->nr_rt_entries)
> > > > > +		hlist_for_each_entry(e, n, &irq_rt->map[irq], link) {
> > > > > +			if (ei->type == KVM_IRQ_ROUTING_MSI)
> > > > > +				ret = kvm_set_msi(e, kvm, irq_source_id, level,
> > > > > +						  host_irq);
> > > > > +			else
> > > > > +				ret = -EWOULDBLOCK;
> > > > > +			break;
> > > > > +		}
> > > > > +	rcu_read_unlock_bh();
> > > > > +	return ret;
> > > > > +}
> > > > > +
> > > > Share implementation with kvm_set_irq().
> > > 
> > > I considered this. There are several reasons not to do it:
> > > - Amount of common code is very small
> > Why? Just pass msi_only flag to kvm_set_irq() and skip an entry if flag is
> > set and entry type is not msi.
> > 
> > > - As it's separate, it's more obvious that it can't block (kvm_set_irq can block)
> > >   We can even tag kvm_set_irq with might_sleep.
> > They can still be two separate function calling common one.
> 
> No, the common code is the surrounding foreach loop,
> the internal if branch is different.
> 
I do not see any complication whatsoever. The reuse it trivial.

--
			Gleb.