Re: [PATCH v2 2/2] vdpa: send CVQ state load commands in parallel

[Hawkins Jiawei]

Sorry for forgetting cc when replying to the email.

On Wed, 17 May 2023 at 16:22, Eugenio Perez Martin <eperezma@redhat.com> wrote:
>
> On Wed, May 17, 2023 at 7:22 AM Jason Wang <jasowang@redhat.com> wrote:
> >
> > On Sat, May 6, 2023 at 10:07 PM Hawkins Jiawei <yin31149@gmail.com> wrote:
> > >
> > > This patch introduces the vhost_vdpa_net_cvq_add() and
> > > refactors the vhost_vdpa_net_load*(), so that QEMU can
> > > send CVQ state load commands in parallel.
> > >
> > > To be more specific, this patch introduces vhost_vdpa_net_cvq_add()
> > > to add SVQ control commands to SVQ and kick the device,
> > > but does not poll the device used buffers. QEMU will not
> > > poll and check the device used buffers in vhost_vdpa_net_load()
> > > until all CVQ state load commands have been sent to the device.
> > >
> > > What's more, in order to avoid buffer overwriting caused by
> > > using `svq->cvq_cmd_out_buffer` and `svq->status` as the
> > > buffer for all CVQ state load commands when sending
> > > CVQ state load commands in parallel, this patch introduces
> > > `out_cursor` and `in_cursor` in vhost_vdpa_net_load(),
> > > pointing to the available buffer for in descriptor and
> > > out descriptor, so that different CVQ state load commands can
> > > use their unique buffer.
> > >
> > > Resolves: https://gitlab.com/qemu-project/qemu/-/issues/1578
> > > Signed-off-by: Hawkins Jiawei <yin31149@gmail.com>
> > > ---
> > >  net/vhost-vdpa.c | 152 +++++++++++++++++++++++++++++++++++++----------
> > >  1 file changed, 120 insertions(+), 32 deletions(-)
> > >
> > > diff --git a/net/vhost-vdpa.c b/net/vhost-vdpa.c
> > > index 10804c7200..14e31ca5c5 100644
> > > --- a/net/vhost-vdpa.c
> > > +++ b/net/vhost-vdpa.c
> > > @@ -590,6 +590,44 @@ static void vhost_vdpa_net_cvq_stop(NetClientState 
> > > *nc)
> > >      vhost_vdpa_net_client_stop(nc);
> > >  }
> > >
> > > +/**
> > > + * vhost_vdpa_net_cvq_add() adds SVQ control commands to SVQ,
> > > + * kicks the device but does not poll the device used buffers.
> > > + *
> > > + * Return the number of elements added to SVQ if success.
> > > + */
> > > +static int vhost_vdpa_net_cvq_add(VhostVDPAState *s,
> > > +                                void **out_cursor, size_t out_len,
> >
> > Can we track things like cursors in e.g VhostVDPAState ?
> >
>
> Cursors will only be used at device startup. After that, cursors are
> always the full buffer. Do we want to "pollute" VhostVDPAState with
> things that will not be used after the startup?
>
> Maybe we can create a struct for them and then pass just this struct?

Yes, Currently, the new version of vhost_vdpa_net_cvq_add() is only
called in vhost_vdpa_net_load() at startup, so these cursors will not be
used after startup.

If needed, we can create a `VhostVDPACursor` as suggested by Eugenio.

>
> Thanks!
>
> > > +                                virtio_net_ctrl_ack **in_cursor, size_t 
> > > in_len)
> > > +{
> > > +    /* Buffers for the device */
> > > +    const struct iovec out = {
> > > +        .iov_base = *out_cursor,
> > > +        .iov_len = out_len,
> > > +    };
> > > +    const struct iovec in = {
> > > +        .iov_base = *in_cursor,
> > > +        .iov_len = sizeof(virtio_net_ctrl_ack),
> > > +    };
> > > +    VhostShadowVirtqueue *svq = 
> > > g_ptr_array_index(s->vhost_vdpa.shadow_vqs, 0);
> > > +    int r;
> > > +
> > > +    r = vhost_svq_add(svq, &out, 1, &in, 1, NULL);
> > > +    if (unlikely(r != 0)) {
> > > +        if (unlikely(r == -ENOSPC)) {
> > > +            qemu_log_mask(LOG_GUEST_ERROR, "%s: No space on device 
> > > queue\n",
> > > +                          __func__);
> > > +        }
> > > +        return r;
> > > +    }
> > > +
> > > +    /* Update the cursor */
> > > +    *out_cursor += out_len;
> > > +    *in_cursor += 1;
> > > +
> > > +    return 1;
> > > +}
> > > +
> > >  /**
> > >   * vhost_vdpa_net_cvq_add_and_wait() adds SVQ control commands to SVQ,
> > >   * kicks the device and polls the device used buffers.
> > > @@ -628,69 +666,82 @@ static ssize_t 
> > > vhost_vdpa_net_cvq_add_and_wait(VhostVDPAState *s,
> > >      return vhost_svq_poll(svq);
> > >  }
> > >
> > > -static ssize_t vhost_vdpa_net_load_cmd(VhostVDPAState *s, uint8_t class,
> > > -                                       uint8_t cmd, const void *data,
> > > -                                       size_t data_size)
> > > +
> > > +/**
> > > + * vhost_vdpa_net_load_cmd() restores the NIC state through SVQ.
> > > + *
> > > + * Return the number of elements added to SVQ if success.
> > > + */
> > > +static int vhost_vdpa_net_load_cmd(VhostVDPAState *s,
> > > +                                void **out_cursor, uint8_t class, 
> > > uint8_t cmd,
> > > +                                const void *data, size_t data_size,
> > > +                                virtio_net_ctrl_ack **in_cursor)
> > >  {
> > >      const struct virtio_net_ctrl_hdr ctrl = {
> > >          .class = class,
> > >          .cmd = cmd,
> > >      };
> > >
> > > -    assert(data_size < vhost_vdpa_net_cvq_cmd_page_len() - sizeof(ctrl));
> > > +    assert(sizeof(ctrl) < vhost_vdpa_net_cvq_cmd_page_len() -
> > > +                          (*out_cursor - s->cvq_cmd_out_buffer));
> > > +    assert(data_size < vhost_vdpa_net_cvq_cmd_page_len() - sizeof(ctrl) -
> > > +                       (*out_cursor - s->cvq_cmd_out_buffer));
> > >
> > > -    memcpy(s->cvq_cmd_out_buffer, &ctrl, sizeof(ctrl));
> > > -    memcpy(s->cvq_cmd_out_buffer + sizeof(ctrl), data, data_size);
> > > +    memcpy(*out_cursor, &ctrl, sizeof(ctrl));
> > > +    memcpy(*out_cursor + sizeof(ctrl), data, data_size);
> > >
> > > -    return vhost_vdpa_net_cvq_add_and_wait(s, sizeof(ctrl) + data_size,
> > > -                                  sizeof(virtio_net_ctrl_ack));
> > > +    return vhost_vdpa_net_cvq_add(s, out_cursor, sizeof(ctrl) + 
> > > data_size,
> > > +                                  in_cursor, 
> > > sizeof(virtio_net_ctrl_ack));
> > >  }
> > >
> > > -static int vhost_vdpa_net_load_mac(VhostVDPAState *s, const VirtIONet *n)
> > > +/**
> > > + * vhost_vdpa_net_load_mac() restores the NIC mac through SVQ.
> > > + *
> > > + * Return the number of elements added to SVQ if success.
> > > + */
> > > +static int vhost_vdpa_net_load_mac(VhostVDPAState *s, const VirtIONet *n,
> > > +                            void **out_cursor, virtio_net_ctrl_ack 
> > > **in_cursor)
> > >  {
> > >      uint64_t features = n->parent_obj.guest_features;
> > >      if (features & BIT_ULL(VIRTIO_NET_F_CTRL_MAC_ADDR)) {
> > > -        ssize_t dev_written = vhost_vdpa_net_load_cmd(s, 
> > > VIRTIO_NET_CTRL_MAC,
> > > -                                                  
> > > VIRTIO_NET_CTRL_MAC_ADDR_SET,
> > > -                                                  n->mac, 
> > > sizeof(n->mac));
> > > -        if (unlikely(dev_written < 0)) {
> > > -            return dev_written;
> > > -        }
> > > -
> > > -        return *s->status != VIRTIO_NET_OK;
> > > +        return vhost_vdpa_net_load_cmd(s, out_cursor, 
> > > VIRTIO_NET_CTRL_MAC,
> > > +                                       VIRTIO_NET_CTRL_MAC_ADDR_SET,
> > > +                                       n->mac, sizeof(n->mac), 
> > > in_cursor);
> > >      }
> > >
> > >      return 0;
> > >  }
> > >
> > > -static int vhost_vdpa_net_load_mq(VhostVDPAState *s,
> > > -                                  const VirtIONet *n)
> > > +/**
> > > + * vhost_vdpa_net_load_mac() restores the NIC mq state through SVQ.
> > > + *
> > > + * Return the number of elements added to SVQ if success.
> > > + */
> > > +static int vhost_vdpa_net_load_mq(VhostVDPAState *s, const VirtIONet *n,
> > > +                            void **out_cursor, virtio_net_ctrl_ack 
> > > **in_cursor)
> > >  {
> > >      struct virtio_net_ctrl_mq mq;
> > >      uint64_t features = n->parent_obj.guest_features;
> > > -    ssize_t dev_written;
> > >
> > >      if (!(features & BIT_ULL(VIRTIO_NET_F_MQ))) {
> > >          return 0;
> > >      }
> > >
> > >      mq.virtqueue_pairs = cpu_to_le16(n->curr_queue_pairs);
> > > -    dev_written = vhost_vdpa_net_load_cmd(s, VIRTIO_NET_CTRL_MQ,
> > > -                                          
> > > VIRTIO_NET_CTRL_MQ_VQ_PAIRS_SET, &mq,
> > > -                                          sizeof(mq));
> > > -    if (unlikely(dev_written < 0)) {
> > > -        return dev_written;
> > > -    }
> > > -
> > > -    return *s->status != VIRTIO_NET_OK;
> > > +    return vhost_vdpa_net_load_cmd(s, out_cursor, VIRTIO_NET_CTRL_MQ,
> > > +                                   VIRTIO_NET_CTRL_MQ_VQ_PAIRS_SET,
> > > +                                   &mq, sizeof(mq), in_cursor);
> > >  }
> > >
> > >  static int vhost_vdpa_net_load(NetClientState *nc)
> > >  {
> > >      VhostVDPAState *s = DO_UPCAST(VhostVDPAState, nc, nc);
> > > +    VhostShadowVirtqueue *svq;
> > > +    void *out_cursor;
> > > +    virtio_net_ctrl_ack *in_cursor;
> > >      struct vhost_vdpa *v = &s->vhost_vdpa;
> > >      const VirtIONet *n;
> > > -    int r;
> > > +    ssize_t cmds_in_flight = 0, dev_written, r;
> > >
> > >      assert(nc->info->type == NET_CLIENT_DRIVER_VHOST_VDPA);
> > >
> > > @@ -699,14 +750,51 @@ static int vhost_vdpa_net_load(NetClientState *nc)
> > >      }
> > >
> > >      n = VIRTIO_NET(v->dev->vdev);
> > > -    r = vhost_vdpa_net_load_mac(s, n);
> > > +    out_cursor = s->cvq_cmd_out_buffer;
> > > +    in_cursor = s->status;
> > > +
> > > +    r = vhost_vdpa_net_load_mac(s, n, &out_cursor, &in_cursor);
> > >      if (unlikely(r < 0))
> > >          return r;
> > >      }
> > > -    r = vhost_vdpa_net_load_mq(s, n);
> > > -    if (unlikely(r)) {
> > > +    cmds_in_flight += r;
> > > +
> > > +    r = vhost_vdpa_net_load_mq(s, n, &out_cursor, &in_cursor);
> > > +    if (unlikely(r < 0)) {
> > >          return r;
> > >      }
> > > +    cmds_in_flight += r;
> > > +
> > > +    /* Poll for all used buffer from device */
> > > +    svq = g_ptr_array_index(s->vhost_vdpa.shadow_vqs, 0);
> > > +    while (cmds_in_flight > 0) {
> > > +        /*
> > > +         * We can poll here since we've had BQL from the time we sent the
> > > +         * descriptor. Also, we need to take the answer before SVQ pulls
> > > +         * by itself, when BQL is released
> > > +         */
> > > +        dev_written = vhost_svq_poll(svq);
> >
> > I'd tweak vhost_svq_poll to accept cmds_in_flight.

That sounds great!
I will refactor the code here and send the v2 patch after
your patch.

Thanks!

> >
> > Thanks
> >
> > > +
> > > +        if (unlikely(!dev_written)) {
> > > +            /*
> > > +             * vhost_svq_poll() return 0 when something wrong, such as
> > > +             * QEMU waits for too long time or no available used buffer
> > > +             * from device, and there is no need to continue polling
> > > +             * in this case.
> > > +             */
> > > +            return -EINVAL;
> > > +        }
> > > +
> > > +        --cmds_in_flight;
> > > +    }
> > > +
> > > +    /* Check the buffers written by device */
> > > +    for (virtio_net_ctrl_ack *status = s->status; status < in_cursor;
> > > +         ++status) {
> > > +        if (*status != VIRTIO_NET_OK) {
> > > +            return -EINVAL;
> > > +        }
> > > +    }
> > >
> > >      return 0;
> > >  }
> > > --
> > > 2.25.1
> > >
> >
>