[Qemu-devel] [RFC PATCH] virtio-mmio: support for multiple irqs

[Shannon Zhao]

As the current virtio-mmio only support single irq,
so some advanced features such as vhost-net with irqfd
are not supported. And the net performance is not
the best without vhost-net and irqfd supporting.

This patch support virtio-mmio to request multiple
irqs like virtio-pci. With this patch and qemu assigning
multiple irqs for virtio-mmio device, it's ok to use
vhost-net with irqfd on arm/arm64.

As arm doesn't support msi-x now, we use GSI for
multiple irq. In this patch we use "vm_try_to_find_vqs"
to check whether multiple irqs are supported like
virtio-pci.

Is this the right direction? is there other ways to
make virtio-mmio support multiple irq? Hope for feedback.
Thanks.

Signed-off-by: Shannon Zhao <address@hidden>
---
 drivers/virtio/virtio_mmio.c |  234 ++++++++++++++++++++++++++++++++++++------
 1 files changed, 203 insertions(+), 31 deletions(-)

diff --git a/drivers/virtio/virtio_mmio.c b/drivers/virtio/virtio_mmio.c
index c600ccf..2b7d935 100644
--- a/drivers/virtio/virtio_mmio.c
+++ b/drivers/virtio/virtio_mmio.c
@@ -122,6 +122,15 @@ struct virtio_mmio_device {
        /* a list of queues so we can dispatch IRQs */
        spinlock_t lock;
        struct list_head virtqueues;
+
+       /* multiple irq support */
+       int single_irq_enabled;
+       /* Number of available irqs */
+       unsigned num_irqs;
+       /* Used number of irqs */
+       int used_irqs;
+       /* Name strings for interrupts. */
+       char (*vm_vq_names)[256];
 };
 
 struct virtio_mmio_vq_info {
@@ -229,33 +238,53 @@ static bool vm_notify(struct virtqueue *vq)
        return true;
 }
 
+/* Handle a configuration change: Tell driver if it wants to know. */
+static irqreturn_t vm_config_changed(int irq, void *opaque)
+{
+       struct virtio_mmio_device *vm_dev = opaque;
+       struct virtio_driver *vdrv = container_of(vm_dev->vdev.dev.driver,
+               struct virtio_driver, driver);
+
+       if (vdrv && vdrv->config_changed)
+               vdrv->config_changed(&vm_dev->vdev);
+       return IRQ_HANDLED;
+}
+
 /* Notify all virtqueues on an interrupt. */
-static irqreturn_t vm_interrupt(int irq, void *opaque)
+static irqreturn_t vm_vring_interrupt(int irq, void *opaque)
 {
        struct virtio_mmio_device *vm_dev = opaque;
        struct virtio_mmio_vq_info *info;
-       struct virtio_driver *vdrv = container_of(vm_dev->vdev.dev.driver,
-                       struct virtio_driver, driver);
-       unsigned long status;
+       irqreturn_t ret = IRQ_NONE;
        unsigned long flags;
+
+       spin_lock_irqsave(&vm_dev->lock, flags);
+       list_for_each_entry(info, &vm_dev->virtqueues, node) {
+               if (vring_interrupt(irq, info->vq) == IRQ_HANDLED)
+                       ret = IRQ_HANDLED;
+       }
+       spin_unlock_irqrestore(&vm_dev->lock, flags);
+
+       return ret;
+}
+
+/* Notify all virtqueues and handle a configuration
+ * change on an interrupt. */
+static irqreturn_t vm_interrupt(int irq, void *opaque)
+{
+       struct virtio_mmio_device *vm_dev = opaque;
+       unsigned long status;
        irqreturn_t ret = IRQ_NONE;
 
        /* Read and acknowledge interrupts */
        status = readl(vm_dev->base + VIRTIO_MMIO_INTERRUPT_STATUS);
        writel(status, vm_dev->base + VIRTIO_MMIO_INTERRUPT_ACK);
 
-       if (unlikely(status & VIRTIO_MMIO_INT_CONFIG)
-                       && vdrv && vdrv->config_changed) {
-               vdrv->config_changed(&vm_dev->vdev);
-               ret = IRQ_HANDLED;
-       }
+       if (unlikely(status & VIRTIO_MMIO_INT_CONFIG))
+               return vm_config_changed(irq, opaque);
 
-       if (likely(status & VIRTIO_MMIO_INT_VRING)) {
-               spin_lock_irqsave(&vm_dev->lock, flags);
-               list_for_each_entry(info, &vm_dev->virtqueues, node)
-                       ret |= vring_interrupt(irq, info->vq);
-               spin_unlock_irqrestore(&vm_dev->lock, flags);
-       }
+       if (likely(status & VIRTIO_MMIO_INT_VRING))
+               return vm_vring_interrupt(irq, opaque);
 
        return ret;
 }
@@ -284,18 +313,98 @@ static void vm_del_vq(struct virtqueue *vq)
        kfree(info);
 }
 
-static void vm_del_vqs(struct virtio_device *vdev)
+static void vm_free_irqs(struct virtio_device *vdev)
 {
+       int i;
        struct virtio_mmio_device *vm_dev = to_virtio_mmio_device(vdev);
+
+       if (vm_dev->single_irq_enabled) {
+               free_irq(platform_get_irq(vm_dev->pdev, 0), vm_dev);
+               vm_dev->single_irq_enabled = 0;
+       }
+
+       for (i = 0; i < vm_dev->used_irqs; ++i)
+               free_irq(platform_get_irq(vm_dev->pdev, i), vm_dev);
+
+       vm_dev->num_irqs = 0;
+       vm_dev->used_irqs = 0;
+       kfree(vm_dev->vm_vq_names);
+       vm_dev->vm_vq_names = NULL;
+}
+
+static void vm_del_vqs(struct virtio_device *vdev)
+{
        struct virtqueue *vq, *n;
 
        list_for_each_entry_safe(vq, n, &vdev->vqs, list)
                vm_del_vq(vq);
 
-       free_irq(platform_get_irq(vm_dev->pdev, 0), vm_dev);
+       vm_free_irqs(vdev);
+}
+
+static int vm_request_multiple_irqs(struct virtio_device *vdev, int nirqs,
+               bool per_vq_irq)
+{
+       int err = -ENOMEM;
+       struct virtio_mmio_device *vm_dev = to_virtio_mmio_device(vdev);
+       unsigned i, v;
+       int irq = 0;
+
+       vm_dev->num_irqs = nirqs;
+       vm_dev->used_irqs = 0;
+
+       vm_dev->vm_vq_names = kmalloc_array(nirqs, sizeof(*vm_dev->vm_vq_names),
+                                    GFP_KERNEL);
+       if (!vm_dev->vm_vq_names)
+               goto error;
+
+       for (i = 0; i < nirqs; i++) {
+               irq = platform_get_irq(vm_dev->pdev, i);
+               if (irq == -ENXIO)
+                       goto error;
+       }
+
+       /* Set the irq used for configuration */
+       v = vm_dev->used_irqs;
+       snprintf(vm_dev->vm_vq_names[v], sizeof(*vm_dev->vm_vq_names),
+                "%s-config", dev_name(&vdev->dev));
+       irq = platform_get_irq(vm_dev->pdev, v);
+       err = request_irq(irq, vm_config_changed, 0,
+               vm_dev->vm_vq_names[v], vm_dev);
+       ++vm_dev->used_irqs;
+       if (err)
+               goto error;
+
+       if (!per_vq_irq) {
+               /* Shared irq for all VQs */
+               v = vm_dev->used_irqs;
+               snprintf(vm_dev->vm_vq_names[v], sizeof(*vm_dev->vm_vq_names),
+                        "%s-virtqueues", dev_name(&vdev->dev));
+               irq = platform_get_irq(vm_dev->pdev, v);
+               err = request_irq(irq, vm_vring_interrupt, 0,
+                       vm_dev->vm_vq_names[v], vm_dev);
+               if (err)
+                       goto error;
+               ++vm_dev->used_irqs;
+       }
+       return 0;
+error:
+       vm_free_irqs(vdev);
+       return err;
 }
 
+static int vm_request_single_irq(struct virtio_device *vdev)
+{
+       int err;
+       struct virtio_mmio_device *vm_dev = to_virtio_mmio_device(vdev);
+       int irq = platform_get_irq(vm_dev->pdev, 0);
 
+       err = request_irq(irq, vm_interrupt, IRQF_SHARED,
+               dev_name(&vdev->dev), vm_dev);
+       if (!err)
+               vm_dev->single_irq_enabled = 1;
+       return err;
+}
 
 static struct virtqueue *vm_setup_vq(struct virtio_device *vdev, unsigned 
index,
                                  void (*callback)(struct virtqueue *vq),
@@ -392,29 +501,92 @@ error_available:
        return ERR_PTR(err);
 }
 
-static int vm_find_vqs(struct virtio_device *vdev, unsigned nvqs,
-                      struct virtqueue *vqs[],
-                      vq_callback_t *callbacks[],
-                      const char *names[])
+static int vm_try_to_find_vqs(struct virtio_device *vdev, unsigned nvqs,
+                             struct virtqueue *vqs[],
+                             vq_callback_t *callbacks[],
+                             const char *names[],
+                             bool use_multiple_irq,
+                             bool per_vq_irq)
 {
        struct virtio_mmio_device *vm_dev = to_virtio_mmio_device(vdev);
-       unsigned int irq = platform_get_irq(vm_dev->pdev, 0);
-       int i, err;
+       int i, err, nirqs, irq;
+
+       if (!use_multiple_irq) {
+               /* Old style: one normal interrupt for change and all vqs. */
+               err = vm_request_single_irq(vdev);
+               if (err)
+                       goto error_request;
+       } else {
+               if (per_vq_irq) {
+                       /* Best option: one for change interrupt, one per vq. */
+                       nirqs = 1;
+                       for (i = 0; i < nvqs; ++i)
+                               if (callbacks[i])
+                                       ++nirqs;
+               } else {
+                       /* Second best: one for change, shared for all vqs. */
+                       nirqs = 2;
+               }
 
-       err = request_irq(irq, vm_interrupt, IRQF_SHARED,
-                       dev_name(&vdev->dev), vm_dev);
-       if (err)
-               return err;
+               err = vm_request_multiple_irqs(vdev, nirqs, per_vq_irq);
+               if (err)
+                       goto error_request;
+       }
 
-       for (i = 0; i < nvqs; ++i) {
+       for (i = 0; i < nvqs; i++) {
+               if (!names[i]) {
+                       vqs[i] = NULL;
+                       continue;
+               }
                vqs[i] = vm_setup_vq(vdev, i, callbacks[i], names[i]);
                if (IS_ERR(vqs[i])) {
-                       vm_del_vqs(vdev);
-                       return PTR_ERR(vqs[i]);
+                       err = PTR_ERR(vqs[i]);
+                       goto error_find;
+               }
+               if (!per_vq_irq || !callbacks[i])
+                       continue;
+               /* allocate per-vq irq if available and necessary */
+               snprintf(vm_dev->vm_vq_names[vm_dev->used_irqs],
+                       sizeof(*vm_dev->vm_vq_names),
+                       "%s-%s",
+                       dev_name(&vm_dev->vdev.dev), names[i]);
+               irq = platform_get_irq(vm_dev->pdev, vm_dev->used_irqs);
+               err = request_irq(irq, vring_interrupt, 0,
+                       vm_dev->vm_vq_names[vm_dev->used_irqs], vqs[i]);
+               if (err) {
+                       vm_del_vq(vqs[i]);
+                       goto error_find;
                }
+               ++vm_dev->used_irqs;
        }
-
        return 0;
+error_find:
+       vm_del_vqs(vdev);
+
+error_request:
+       return err;
+}
+
+static int vm_find_vqs(struct virtio_device *vdev, unsigned nvqs,
+                      struct virtqueue *vqs[],
+                      vq_callback_t *callbacks[],
+                      const char *names[])
+{
+       int err;
+
+       /* Try multiple irqs with one irq per queue. */
+       err = vm_try_to_find_vqs(vdev, nvqs, vqs, callbacks, names, true, true);
+       if (!err)
+               return 0;
+       /* Fallback: multiple irqs with one irq for config,
+        * one shared for queues. */
+       err = vm_try_to_find_vqs(vdev, nvqs, vqs, callbacks, names,
+                                true, false);
+       if (!err)
+               return 0;
+       /* Finally fall back to regular single interrupts. */
+       return vm_try_to_find_vqs(vdev, nvqs, vqs, callbacks, names,
+                                 false, false);
 }
 
 static const char *vm_bus_name(struct virtio_device *vdev)
-- 
1.7.1