Re: [PATCH 3/3] virtio-pci: don't poll masked vectors

Michael S. Tsirkin
2012-12-19T11:25:59Z

On Wed, Dec 19, 2012 at 04:59:05PM +0800, Asias He wrote:
> On 12/18/2012 08:39 PM, Michael S. Tsirkin wrote:
> > At the moment, when irqfd is in use but a vector is masked,
> > qemu will poll it and handle vector masks in userspace.
> > Since almost no one ever looks at the pending bits,
> > it is better to defer this until pending bits
> > are actually read.
> > Implement this optimization using the new poll notifier.
> >
> > Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
> > ---
> > hw/virtio-pci.c | 52 ++++++++++++++++++++++++++++++++++++++++------------
> > 1 file changed, 40 insertions(+), 12 deletions(-)
> >
> > diff --git a/hw/virtio-pci.c b/hw/virtio-pci.c
> > index 1c03bb5..bc6b4e0 100644
> > --- a/hw/virtio-pci.c
> > +++ b/hw/virtio-pci.c
> > @@ -509,8 +509,6 @@ static int kvm_virtio_pci_vq_vector_use(VirtIOPCIProxy *proxy,
> > }
> > return ret;
> > }
> > -
> > - virtio_queue_set_guest_notifier_fd_handler(vq, true, true);
> > return 0;
> > }
> >
> > @@ -529,8 +527,6 @@ static void kvm_virtio_pci_vq_vector_release(VirtIOPCIProxy *proxy,
> > if (--irqfd->users == 0) {
> > kvm_irqchip_release_virq(kvm_state, irqfd->virq);
> > }
> > -
> > - virtio_queue_set_guest_notifier_fd_handler(vq, true, false);
> > }
> >
> > static int kvm_virtio_pci_vector_use(PCIDevice *dev, unsigned vector,
> > @@ -581,7 +577,36 @@ static void kvm_virtio_pci_vector_release(PCIDevice *dev, unsigned vector)
> > }
> > }
> >
> > -static int virtio_pci_set_guest_notifier(DeviceState *d, int n, bool assign)
> > +static void kvm_virtio_pci_vector_poll(PCIDevice *dev,
> > + unsigned int vector_start,
> > + unsigned int vector_end)
> > +{
> > + VirtIOPCIProxy *proxy = container_of(dev, VirtIOPCIProxy, pci_dev);
> > + VirtIODevice *vdev = proxy->vdev;
> > + int queue_no;
> > + unsigned int vector;
> > + EventNotifier *notifier;
> > + VirtQueue *vq;
> > +
> > + for (queue_no = 0; queue_no < VIRTIO_PCI_QUEUE_MAX; queue_no++) {
> > + if (!virtio_queue_get_num(vdev, queue_no)) {
> > + break;
> > + }
> > + vector = virtio_queue_vector(vdev, queue_no);
> > + if (vector < vector_start || vector >= vector_end ||
> > + !msix_is_masked(dev, vector)) {
> > + continue;
> > + }
> > + vq = virtio_get_queue(vdev, queue_no);
> > + notifier = virtio_queue_get_guest_notifier(vq);
> > + if (event_notifier_test_and_clear(notifier)) {
> > + msix_set_pending(dev, vector);
> > + }
> > + }
> > +}
> > +
> > +static int virtio_pci_set_guest_notifier(DeviceState *d, int n, bool assign,
> > + bool with_irqfd)
> > {
> > VirtIOPCIProxy *proxy = to_virtio_pci_proxy(d);
> > VirtQueue *vq = virtio_get_queue(proxy->vdev, n);
> > @@ -592,9 +617,9 @@ static int virtio_pci_set_guest_notifier(DeviceState *d, int n, bool assign)
> > if (r < 0) {
> > return r;
> > }
> > - virtio_queue_set_guest_notifier_fd_handler(vq, true, false);
> > + virtio_queue_set_guest_notifier_fd_handler(vq, true, with_irqfd);
>
> + virtio_queue_set_guest_notifier_fd_handler(vq, assign, with_irqfd);
>
> > } else {
> > - virtio_queue_set_guest_notifier_fd_handler(vq, false, false);
> > + virtio_queue_set_guest_notifier_fd_handler(vq, false, with_irqfd);
>
> + virtio_queue_set_guest_notifier_fd_handler(vq, assign, with_irqfd);
>
> Use the 'assign' variable instead of the constants?

I don't care either way (this is within if (assign)).
But all this patch does is add a parameter,
unrelated code refactorings should be separate.

> > event_notifier_cleanup(notifier);
> > }
> >
> > @@ -612,9 +637,11 @@ static int virtio_pci_set_guest_notifiers(DeviceState *d, bool assign)
> > VirtIOPCIProxy *proxy = to_virtio_pci_proxy(d);
> > VirtIODevice *vdev = proxy->vdev;
> > int r, n;
> > + bool with_irqfd = msix_enabled(&proxy->pci_dev) &&
> > + kvm_msi_via_irqfd_enabled();
> >
> > /* Must unset vector notifier while guest notifier is still assigned */
> > - if (kvm_msi_via_irqfd_enabled() && !assign) {
> > + if (with_irqfd && !assign) {
> > msix_unset_vector_notifiers(&proxy->pci_dev);
> > g_free(proxy->vector_irqfd);
> > proxy->vector_irqfd = NULL;
> > @@ -625,21 +652,22 @@ static int virtio_pci_set_guest_notifiers(DeviceState *d, bool assign)
> > break;
> > }
> >
> > - r = virtio_pci_set_guest_notifier(d, n, assign);
> > + r = virtio_pci_set_guest_notifier(d, n, assign,
> > + kvm_msi_via_irqfd_enabled());
> > if (r < 0) {
> > goto assign_error;
> > }
> > }
> >
> > /* Must set vector notifier after guest notifier has been assigned */
> > - if (kvm_msi_via_irqfd_enabled() && assign) {
> > + if (with_irqfd && assign) {
> > proxy->vector_irqfd =
> > g_malloc0(sizeof(*proxy->vector_irqfd) *
> > msix_nr_vectors_allocated(&proxy->pci_dev));
> > r = msix_set_vector_notifiers(&proxy->pci_dev,
> > kvm_virtio_pci_vector_use,
> > kvm_virtio_pci_vector_release,
> > - NULL);
> > + kvm_virtio_pci_vector_poll);
> > if (r < 0) {
> > goto assign_error;
> > }
> > @@ -651,7 +679,7 @@ assign_error:
> > /* We get here on assignment failure. Recover by undoing for VQs 0 .. n. */
> > assert(assign);
> > while (--n >= 0) {
> > - virtio_pci_set_guest_notifier(d, n, !assign);
> > + virtio_pci_set_guest_notifier(d, n, !assign, with_irqfd);
> > }
> > return r;
> > }
> >
>
>
> --
> Asias