On Tue, Jan 25, 2011 at 01:58:08PM +0000, Stefan Hajnoczi wrote:
> It is not possible to use virtio-ioeventfd when building without an I/O
> thread. We rely on a signal to kick us out of vcpu execution. Timers
> and AIO use SIGALRM and SIGUSR2 respectively. Unfortunately eventfd
> does not support O_ASYNC (SIGIO) so eventfd cannot be used in a signal
> driven manner.
>
> Signed-off-by: Stefan Hajnoczi <stefa...@linux.vnet.ibm.com>
I'd rather have the CONFIG_ ... mess contained in kvm-all.c
which tests CONFIG_IOTHREAD anyway, than spread out
to devices. Can we make kvm_has_many_ioeventfds check this?
> ---
> hw/virtio-pci.c | 21 ++++++++++++++++++++-
> 1 files changed, 20 insertions(+), 1 deletions(-)
>
> diff --git a/hw/virtio-pci.c b/hw/virtio-pci.c
> index d07ff97..e921eda 100644
> --- a/hw/virtio-pci.c
> +++ b/hw/virtio-pci.c
> @@ -640,6 +640,25 @@ static int virtio_pci_set_host_notifier(void *opaque,
> int n, bool assign)
> return virtio_pci_set_host_notifier_internal(proxy, n, assign);
> }
>
> +static bool virtio_pci_can_use_ioeventfd(void)
> +{
> + if (!kvm_has_many_ioeventfds()) {
> + return false;
> + }
> +
> + /* Use ioeventfd for virtqueue kick only if we have an I/O thread to
> + * perform out-of-line processing. Otherwise we might as well do
> + * synchronous virtqueue kicks and in fact we have to since eventfd does
> + * not support SIGIO. Without the I/O thread a signal would be required
> to
> + * kick the vcpu out of guest code.
> + */
> +#ifdef CONFIG_IOTHREAD
> + return true;
> +#else
> + return false;
> +#endif
> +}
> +
> static void virtio_pci_vmstate_change(void *opaque, bool running)
> {
> VirtIOPCIProxy *proxy = opaque;
> @@ -705,7 +724,7 @@ static void virtio_init_pci(VirtIOPCIProxy *proxy,
> VirtIODevice *vdev,
> pci_register_bar(&proxy->pci_dev, 0, size, PCI_BASE_ADDRESS_SPACE_IO,
> virtio_map);
>
> - if (!kvm_has_many_ioeventfds()) {
> + if (!virtio_pci_can_use_ioeventfd()) {
> proxy->flags &= ~VIRTIO_PCI_FLAG_USE_IOEVENTFD;
> }
>
> --
> 1.7.2.3
