On Mon, Dec 7, 2020 at 3:03 PM Saeed Mahameed <saeed@xxxxxxxxxx> wrote:
>
> On Mon, 2020-12-07 at 13:16 -0800, Alexander Duyck wrote:
> > On Mon, Dec 7, 2020 at 8:36 AM Lorenzo Bianconi <lorenzo@xxxxxxxxxx>
> > wrote:
> > > Introduce multi-buffer bit (mb) in xdp_frame/xdp_buffer data
> > > structure
> > > in order to specify if this is a linear buffer (mb = 0) or a multi-
> > > buffer
> > > frame (mb = 1). In the latter case the shared_info area at the end
> > > of the
> > > first buffer is been properly initialized to link together
> > > subsequent
> > > buffers.
> > >
> > > Signed-off-by: Lorenzo Bianconi <lorenzo@xxxxxxxxxx>
> > > ---
> > > include/net/xdp.h | 8 ++++++--
> > > net/core/xdp.c | 1 +
> > > 2 files changed, 7 insertions(+), 2 deletions(-)
> > >
> > > diff --git a/include/net/xdp.h b/include/net/xdp.h
> > > index 700ad5db7f5d..70559720ff44 100644
> > > --- a/include/net/xdp.h
> > > +++ b/include/net/xdp.h
> > > @@ -73,7 +73,8 @@ struct xdp_buff {
> > > void *data_hard_start;
> > > struct xdp_rxq_info *rxq;
> > > struct xdp_txq_info *txq;
> > > - u32 frame_sz; /* frame size to deduce
> > > data_hard_end/reserved tailroom*/
> > > + u32 frame_sz:31; /* frame size to deduce
> > > data_hard_end/reserved tailroom*/
> > > + u32 mb:1; /* xdp non-linear buffer */
> > > };
> > >
> >
> > If we are really going to do something like this I say we should just
> > rip a swath of bits out instead of just grabbing one. We are already
> > cutting the size down then we should just decide on the minimum size
> > that is acceptable and just jump to that instead of just stealing one
> > bit at a time. It looks like we already have differences between the
> > size here and frame_size in xdp_frame.
> >
>
> +1
>
> > If we have to steal a bit why not look at something like one of the
> > lower 2/3 bits in rxq? You could then do the same thing using dev_rx
> > in a similar fashion instead of stealing from a bit that is likely to
> > be used in multiple spots and modifying like this adds extra overhead
> > to?
> >
>
> What do you mean in rxq ? from the pointer ?
Yeah, the pointers have a few bits that are guaranteed 0 and in my
mind reusing the lower bits from a 4 or 8 byte aligned pointer would
make more sense then stealing the upper bits from the size of the
frame.
