Re: [PATCH v7] virtio_net: support split header

[Jason Wang <jasowang@redhat.com>]

å 2022/9/5 04:27, Michael S. Tsirkin åé:
> On Fri, Sep 02, 2022 at 03:36:25PM +0800, Heng Qi wrote:
> > We need to clarify that the purpose of header splitting is to make all payloads
> > can be independently in a page, which is beneficial for the zerocopy
> > implemented by the upper layer.
> absolutely, pls add motivation.
>
> > If the driver does not enforce that the buffers submitted to the receiveq MUST
> > be composed of at least two descriptors, then header splitting will become meaningless,
> > or the VIRTIO_NET_F_SPLIT_TRANSPORT_HEADER feature should not be negotiated at this time.
> >
> >
> > Thanks.
>
> This seems very narrow and unecessarily wasteful of descriptors.
> What is wrong in this:
>
> <header>...<padding>... <beginning of page><data>
>
> seems to achieve the goal of data in a separate page without
> using extra descriptors.
>
> thus my proposal to replace the requirement of a separate
> descriptor with an offset of data from beginning of
> buffer that driver sets.


Not sure I get this, does it mean the header and padding are placed at 
the tail of the previous adjacent page?

Thanks


>