Re: [dpdk-dev] [PATCH v3] vhost: read last used index once

[Balazs Nemeth <bnemeth@redhat.com>]

Hi Ling,

I will take a look. Thanks for reporting.

Regards,
Balazs

On Sat, May 8, 2021 at 10:44 AM Ling, WeiX <weix.ling@intel.com> wrote:

> Hi  Balazs Nemeth,
>
> Your patch cause a bug about virtio-user can't recieve packets when use
> packed ring and ring size is 255.
>
> Please have a look about it.
>
> https://bugs.dpdk.org/show_bug.cgi?id=699
>
> Thanks.
>
> Regards,
> Ling Wei
>
> > -----Original Message-----
> > From: dev <dev-bounces@dpdk.org> On Behalf Of Balazs Nemeth
> > Sent: Wednesday, April 7, 2021 05:55 PM
> > To: bnemeth@redhat.com; dev@dpdk.org
> > Subject: [dpdk-dev] [PATCH v3] vhost: read last used index once
> >
> > Instead of calculating the address of a packed descriptor based on the
> > vq->desc_packed and vq->last_used_idx every time, store that base
> > address in desc_base. On arm, this saves 176 bytes in code size of
> function in
> > which vhost_flush_enqueue_batch_packed gets inlined.
> >
> > Signed-off-by: Balazs Nemeth <bnemeth@redhat.com>
> > ---
> >  lib/librte_vhost/virtio_net.c | 13 ++++++++-----
> >  1 file changed, 8 insertions(+), 5 deletions(-)
> >
> > diff --git a/lib/librte_vhost/virtio_net.c
> b/lib/librte_vhost/virtio_net.c index
> > 179c57b46..f091384a6 100644
> > --- a/lib/librte_vhost/virtio_net.c
> > +++ b/lib/librte_vhost/virtio_net.c
> > @@ -217,6 +217,8 @@ vhost_flush_enqueue_batch_packed(struct
> > virtio_net *dev,  {
> >       uint16_t i;
> >       uint16_t flags;
> > +     uint16_t last_used_idx = vq->last_used_idx;
> > +     struct vring_packed_desc *desc_base = &vq-
> > >desc_packed[last_used_idx];
> >
> >       if (vq->shadow_used_idx) {
> >               do_data_copy_enqueue(dev, vq);
> > @@ -226,16 +228,17 @@ vhost_flush_enqueue_batch_packed(struct
> > virtio_net *dev,
> >       flags = PACKED_DESC_ENQUEUE_USED_FLAG(vq-
> > >used_wrap_counter);
> >
> >       vhost_for_each_try_unroll(i, 0, PACKED_BATCH_SIZE) {
> > -             vq->desc_packed[vq->last_used_idx + i].id = ids[i];
> > -             vq->desc_packed[vq->last_used_idx + i].len = lens[i];
> > +             desc_base[i].id = ids[i];
> > +             desc_base[i].len = lens[i];
> >       }
> >
> >       rte_atomic_thread_fence(__ATOMIC_RELEASE);
> >
> > -     vhost_for_each_try_unroll(i, 0, PACKED_BATCH_SIZE)
> > -             vq->desc_packed[vq->last_used_idx + i].flags = flags;
> > +     vhost_for_each_try_unroll(i, 0, PACKED_BATCH_SIZE) {
> > +             desc_base[i].flags = flags;
> > +     }
> >
> > -     vhost_log_cache_used_vring(dev, vq, vq->last_used_idx *
> > +     vhost_log_cache_used_vring(dev, vq, last_used_idx *
> >                                  sizeof(struct vring_packed_desc),
> >                                  sizeof(struct vring_packed_desc) *
> >                                  PACKED_BATCH_SIZE);
> > --
> > 2.30.2
>
>