On Thu, Jan 20, 2011 at 08:31:53AM -0800, Sridhar Samudrala wrote:
> 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.
> >
> > 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?
>
> Should this error be EVHOST_DISABLED rather than EVIRTIO_DISABLED?
>
> -Sridhar
The error is reported by virtio-pci which does not know about vhost.
I started with EVIRTIO_MSIX_DISABLED and made is shorter.
Would EVIRTIO_MSIX_DISABLED be better?
> >
> > 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);
> > + }
> > 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
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