Re: [libvirt] [PATCH] kvm/virtio: Set IFF_VNET_HDR when setting up tap fds
On Wed, 2008-08-13 at 16:01 +0100, Daniel P. Berrange wrote:
On Wed, Aug 13, 2008 at 03:53:27PM +0100, Mark McLoughlin wrote:
> By enabling this flag on the tap fds we create, we greatly increase
> the achievable throughput with virtio_net.
>
> However, we need to be careful to only set the flag when a) KVM has
> support for this ABI and b) the value of the flag is queryable using
> the TUNGETIFF ioctl.
This suggests to me that QEMU should be a the one enabling this
flag, not libvirt.
It has to be done before adding it to the bridge and can't be changed
afterwards.
(Which perhaps suggests the kernel API is a little dumb, but ...)
Its going to need todo this anyway for the
scenario where QEMU allocates the TAP fd, so it might as well
enable it for pre-allocated TAP fds passed in from external
apps.
Yeah, it already does it for the fds it allocates.
Cheers,
Mark.