Commit f1d0f15a authored by Michael S. Tsirkin's avatar Michael S. Tsirkin
Browse files

virtio: backend virtqueue notifier masking 



some backends (notably vhost) can mask events
at their source in a way that is more efficient
than masking through kvm.
Specifically
- masking in kvm uses rcu write side so it has high latency
- in kvm on unmask we always send an interrupt
masking at source does not have these issues.

Add such support in virtio.h and use in virtio-pci.

Signed-off-by: default avatarMichael S. Tsirkin <mst@redhat.com>
parent 774345f9

hw/virtio-pci.c

+70 −9
Original line number Diff line number Diff line
@@ -510,6 +510,31 @@ static void kvm_virtio_pci_vq_vector_release(VirtIOPCIProxy *proxy, 
    }

}



static int kvm_virtio_pci_irqfd_use(VirtIOPCIProxy *proxy,

                                 unsigned int queue_no,

                                 unsigned int vector)

{

    VirtIOIRQFD *irqfd = &proxy->vector_irqfd[vector];

    VirtQueue *vq = virtio_get_queue(proxy->vdev, queue_no);

    EventNotifier *n = virtio_queue_get_guest_notifier(vq);

    int ret;

    ret = kvm_irqchip_add_irqfd_notifier(kvm_state, n, irqfd->virq);

    return ret;

}



static void kvm_virtio_pci_irqfd_release(VirtIOPCIProxy *proxy,

                                      unsigned int queue_no,

                                      unsigned int vector)

{

    VirtQueue *vq = virtio_get_queue(proxy->vdev, queue_no);

    EventNotifier *n = virtio_queue_get_guest_notifier(vq);

    VirtIOIRQFD *irqfd = &proxy->vector_irqfd[vector];

    int ret;



    ret = kvm_irqchip_remove_irqfd_notifier(kvm_state, n, irqfd->virq);

    assert(ret == 0);

}



static int kvm_virtio_pci_vector_use(VirtIOPCIProxy *proxy, int nvqs)

{

    PCIDevice *dev = &proxy->pci_dev;
@@ -531,6 +556,16 @@ static int kvm_virtio_pci_vector_use(VirtIOPCIProxy *proxy, int nvqs) 
        if (ret < 0) {

            goto undo;

        }

        /* If guest supports masking, set up irqfd now.

         * Otherwise, delay until unmasked in the frontend.

         */

        if (proxy->vdev->guest_notifier_mask) {

            ret = kvm_virtio_pci_irqfd_use(proxy, queue_no, vector);

            if (ret < 0) {

                kvm_virtio_pci_vq_vector_release(proxy, vector);

                goto undo;

            }

        }

    }

    return 0;
@@ -540,6 +575,9 @@ undo: 
        if (vector >= msix_nr_vectors_allocated(dev)) {

            continue;

        }

        if (proxy->vdev->guest_notifier_mask) {

            kvm_virtio_pci_irqfd_release(proxy, vector, queue_no);

        }

        kvm_virtio_pci_vq_vector_release(proxy, vector);

    }

    return ret;
@@ -560,6 +598,12 @@ static void kvm_virtio_pci_vector_release(VirtIOPCIProxy *proxy, int nvqs) 
        if (vector >= msix_nr_vectors_allocated(dev)) {

            continue;

        }

        /* If guest supports masking, clean up irqfd now.

         * Otherwise, it was cleaned when masked in the frontend.

         */

        if (proxy->vdev->guest_notifier_mask) {

            kvm_virtio_pci_irqfd_release(proxy, vector, queue_no);

        }

        kvm_virtio_pci_vq_vector_release(proxy, vector);

    }

}
@@ -581,7 +625,19 @@ static int kvm_virtio_pci_vq_vector_unmask(VirtIOPCIProxy *proxy, 
        }

    }



    ret = kvm_irqchip_add_irqfd_notifier(kvm_state, n, irqfd->virq);

    /* If guest supports masking, irqfd is already setup, unmask it.

     * Otherwise, set it up now.

     */

    if (proxy->vdev->guest_notifier_mask) {

        proxy->vdev->guest_notifier_mask(proxy->vdev, queue_no, false);

        /* Test after unmasking to avoid losing events. */

        if (proxy->vdev->guest_notifier_pending &&

            proxy->vdev->guest_notifier_pending(proxy->vdev, queue_no)) {

            event_notifier_set(n);

        }

    } else {

        ret = kvm_virtio_pci_irqfd_use(proxy, queue_no, vector);

    }

    return ret;

}
@@ -589,13 +645,14 @@ static void kvm_virtio_pci_vq_vector_mask(VirtIOPCIProxy *proxy, 
                                             unsigned int queue_no,

                                             unsigned int vector)

{

    VirtQueue *vq = virtio_get_queue(proxy->vdev, queue_no);

    EventNotifier *n = virtio_queue_get_guest_notifier(vq);

    VirtIOIRQFD *irqfd = &proxy->vector_irqfd[vector];

    int ret;



    ret = kvm_irqchip_remove_irqfd_notifier(kvm_state, n, irqfd->virq);

    assert(ret == 0);

    /* If guest supports masking, keep irqfd but mask it.

     * Otherwise, clean it up now.

     */ 

    if (proxy->vdev->guest_notifier_mask) {

        proxy->vdev->guest_notifier_mask(proxy->vdev, queue_no, true);

    } else {

        kvm_virtio_pci_irqfd_release(proxy, vector, queue_no);

    }

}



static int kvm_virtio_pci_vector_unmask(PCIDevice *dev, unsigned vector,
@@ -668,7 +725,11 @@ static void kvm_virtio_pci_vector_poll(PCIDevice *dev, 
        }

        vq = virtio_get_queue(vdev, queue_no);

        notifier = virtio_queue_get_guest_notifier(vq);

        if (event_notifier_test_and_clear(notifier)) {

        if (vdev->guest_notifier_pending) {

            if (vdev->guest_notifier_pending(vdev, queue_no)) {

                msix_set_pending(dev, vector);

            }

        } else if (event_notifier_test_and_clear(notifier)) {

            msix_set_pending(dev, vector);

        }

    }

hw/virtio.h

+13 −0
Original line number Diff line number Diff line
@@ -126,6 +126,19 @@ struct VirtIODevice 
    void (*set_config)(VirtIODevice *vdev, const uint8_t *config);

    void (*reset)(VirtIODevice *vdev);

    void (*set_status)(VirtIODevice *vdev, uint8_t val);

    /* Test and clear event pending status.

     * Should be called after unmask to avoid losing events.

     * If backend does not support masking,

     * must check in frontend instead.

     */

    bool (*guest_notifier_pending)(VirtIODevice *vdev, int n);

    /* Mask/unmask events from this vq. Any events reported

     * while masked will become pending.

     * If backend does not support masking,

     * must mask in frontend instead.

     */

    void (*guest_notifier_mask)(VirtIODevice *vdev, int n, bool mask);



    VirtQueue *vq;

    const VirtIOBindings *binding;

    DeviceState *binding_opaque;