On Tue, Mar 19, 2019 at 10:44:32AM +0100, Jens Freimann wrote:
> On Tue, Mar 19, 2019 at 02:43:07PM +0800, Tiwei Bie wrote:
> > Put split ring and packed ring specific fields into separate
> > sub-structures, and also union them as they won't be available
> > at the same time.
> >
> > Signed-off-by: Tiwei Bie <tiwei....@intel.com>
> > ---
> > drivers/net/virtio/virtio_ethdev.c | 71 +++++++++---------
> > drivers/net/virtio/virtio_rxtx.c | 66 ++++++++---------
> > drivers/net/virtio/virtio_rxtx_simple.h | 2 +-
> > drivers/net/virtio/virtio_rxtx_simple_neon.c | 2 +-
> > drivers/net/virtio/virtio_rxtx_simple_sse.c | 2 +-
> > drivers/net/virtio/virtqueue.c | 6 +-
> > drivers/net/virtio/virtqueue.h | 77 +++++++++++---------
> > 7 files changed, 117 insertions(+), 109 deletions(-)
> >
> [snip]
> ...
> > diff --git a/drivers/net/virtio/virtqueue.h b/drivers/net/virtio/virtqueue.h
> > index 80c0c43c3..48b3912e6 100644
> > --- a/drivers/net/virtio/virtqueue.h
> > +++ b/drivers/net/virtio/virtqueue.h
> > @@ -191,17 +191,22 @@ struct vq_desc_extra {
> >
> > struct virtqueue {
> > struct virtio_hw *hw; /**< virtio_hw structure pointer. */
> > - struct vring vq_ring; /**< vring keeping desc, used and avail */
> > - struct vring_packed ring_packed; /**< vring keeping descs */
> > - bool used_wrap_counter;
> > - uint16_t cached_flags; /**< cached flags for descs */
> > - uint16_t event_flags_shadow;
> > + union {
> > + struct {
> > + /**< vring keeping desc, used and avail */
> > + struct vring ring;
> > + } vq_split;
> >
> > - /**
> > - * Last consumed descriptor in the used table,
> > - * trails vq_ring.used->idx.
> > - */
> > - uint16_t vq_used_cons_idx;
> > + struct {
> > + /**< vring keeping descs and events */
> > + struct vring_packed ring;
> > + bool used_wrap_counter;
> > + uint16_t cached_flags; /**< cached flags for descs */
> > + uint16_t event_flags_shadow;
> > + } vq_packed;
> > + };
> > +
> > + uint16_t vq_used_cons_idx; /**< last consumed descriptor */
> > uint16_t vq_nentries; /**< vring desc numbers */
> > uint16_t vq_free_cnt; /**< num of desc available */
> > uint16_t vq_avail_idx; /**< sync until needed */
>
> Honest question: What do we really gain by putting it in a union? We
> save a little memory. But we also make code less readable IMHO.
I think it will make it clear that fields like used_wrap_counter
are only available in packed ring which will make the code more
readable.
>
> If we do this, can we at least shorten some variable names, like drop
> the vq_ prefix? (It's used everywhere like vq->vq_packed*, so with
> vq->packed* we don't loose any context).
I prefer to have consistent prefix like most fields in this
structure (although some fields don't really follow this).
Thanks,
Tiwei
>
> I'm not strictly against this change but I'm wondering if it's worth
> it.
>
> regards,
> Jens
>
