On Thu, 2011-01-20 at 17:35 +0200, Michael S. Tsirkin wrote:
> When MSI is off, each interrupt needs to be bounced through the io
> thread when it's set/cleared, so vhost-net causes more context switches and
> higher CPU utilization than userspace virtio which handles networking in
> the same thread.
>
> We'll need to fix this by adding level irq support in kvm irqfd,
> for now disable vhost-net in these configurations.
We need this if we want avoid bouncing vfio INtx through qemu too.
> Signed-off-by: Michael S. Tsirkin <mst@xxxxxxxxxx>
> ---
>
> I need to report some error from virtio-pci
> that would be handled specially (disable but don't
> report an error) so I wanted one that's never likely to be used by a
> userspace ioctl. I selected ERANGE but it'd
> be easy to switch to something else. Comments?
>
> hw/vhost.c | 4 +++-
> hw/virtio-net.c | 6 ++++--
> hw/virtio-pci.c | 3 +++
> hw/virtio.h | 2 ++
> 4 files changed, 12 insertions(+), 3 deletions(-)
>
> diff --git a/hw/vhost.c b/hw/vhost.c
> index 1d09ed0..c79765a 100644
> --- a/hw/vhost.c
> +++ b/hw/vhost.c
> @@ -649,7 +649,9 @@ int vhost_dev_start(struct vhost_dev *hdev, VirtIODevice *vdev)
>
> r = vdev->binding->set_guest_notifiers(vdev->binding_opaque, true);
> if (r < 0) {
> - fprintf(stderr, "Error binding guest notifier: %d\n", -r);
> + if (r != -EVIRTIO_DISABLED) {
> + fprintf(stderr, "Error binding guest notifier: %d\n", -r);
> + }
style - the above is tab indented.
> goto fail_notifiers;
> }
>
> diff --git a/hw/virtio-net.c b/hw/virtio-net.c
> index ccb3e63..5de3fee 100644
> --- a/hw/virtio-net.c
> +++ b/hw/virtio-net.c
> @@ -121,8 +121,10 @@ static void virtio_net_vhost_status(VirtIONet *n, uint8_t status)
> if (!n->vhost_started) {
> int r = vhost_net_start(tap_get_vhost_net(n->nic->nc.peer), &n->vdev);
> if (r < 0) {
> - error_report("unable to start vhost net: %d: "
> - "falling back on userspace virtio", -r);
> + if (r != -EVIRTIO_DISABLED) {
> + error_report("unable to start vhost net: %d: "
> + "falling back on userspace virtio", -r);
> + }
> } else {
> n->vhost_started = 1;
> }
> diff --git a/hw/virtio-pci.c b/hw/virtio-pci.c
> index dd8887a..dbf4be0 100644
> --- a/hw/virtio-pci.c
> +++ b/hw/virtio-pci.c
> @@ -628,6 +628,9 @@ static int virtio_pci_set_guest_notifier(void *opaque, int n, bool assign)
> EventNotifier *notifier = virtio_queue_get_guest_notifier(vq);
>
> if (assign) {
> + if (!msix_enabled(&proxy->pci_dev)) {
> + return -EVIRTIO_DISABLED;
> + }
> int r = event_notifier_init(notifier, 0);
> if (r < 0) {
> return r;
> diff --git a/hw/virtio.h b/hw/virtio.h
> index d8546d5..53bbdba 100644
> --- a/hw/virtio.h
> +++ b/hw/virtio.h
> @@ -98,6 +98,8 @@ typedef struct {
> void (*vmstate_change)(void * opaque, bool running);
> } VirtIOBindings;
>
> +#define EVIRTIO_DISABLED ERANGE
> +
> #define VIRTIO_PCI_QUEUE_MAX 64
>
> #define VIRTIO_NO_VECTOR 0xffff
I'm not a fan of having this special return value. Why doesn't
virtio-pci only setup the set_guest_notifiers function pointer when msix
is enabled? If not that, it could at least expose some
virtio_foo_enabled() type feature that vhost could check. Thanks,
Alex
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