On Mon, Jan 07, 2013 at 03:17:18PM -0600, Anthony Liguori wrote:
> "Michael S. Tsirkin" <m...@redhat.com> writes:
>
> > On Mon, Jan 07, 2013 at 07:40:32PM +0100, fred.kon...@greensocs.com wrote:
> >> @@ -130,7 +124,9 @@ static void virtio_net_set_status(struct VirtIODevice
> >> *vdev, uint8_t status)
> >>
> >> static void virtio_net_set_link_status(NetClientState *nc)
> >> {
> >> - VirtIONet *n = DO_UPCAST(NICState, nc, nc)->opaque;
> >> + void *opaque = DO_UPCAST(NICState, nc, nc)->opaque;
> >> + VirtIONet *n = VIRTIO_NET(opaque);
> >> + VirtIODevice *vdev = VIRTIO_DEVICE(n);
> >> uint16_t old_status = n->status;
> >>
> >> if (nc->link_down)
> >
> > I note this adds more pointer chasing due to runtime casts on data path
> > operations. Can well be trivial but this really needs to be verified
> > with a performance test. Was this done? Same comment applies to block.
> > An alternative is to add _fast casts without runtime checks.
>
> I'm pretty sure other things like the one big global mutex are more
> important than the number of pointer dereferences...
True. But we have plans to fix that, right?
> Do you have any evidence to suggest that this would be a problem in practice?
>
> Regards,
>
> Anthony Liguori
No. It's not this change specifically, I'm generally concerned if we let
ourselves bloat datapath in an uncontrolled way, the waste will add up
over time.
> >
> > --
> > MST
