netdev - Re: [RFC 3/5] vhost_test: batch used buffer

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Date:   Fri, 22 Jul 2022 09:12:47 +0200
From:   Eugenio Perez Martin <eperezma@...hat.com>
To:     Guo Zhi <qtxuning1999@...u.edu.cn>
Cc:     Jason Wang <jasowang@...hat.com>,
        Stefano Garzarella <sgarzare@...hat.com>,
        Michael Tsirkin <mst@...hat.com>,
        netdev <netdev@...r.kernel.org>,
        linux-kernel <linux-kernel@...r.kernel.org>,
        kvm list <kvm@...r.kernel.org>,
        virtualization <virtualization@...ts.linux-foundation.org>
Subject: Re: [RFC 3/5] vhost_test: batch used buffer

On Thu, Jul 21, 2022 at 10:44 AM Guo Zhi <qtxuning1999@...u.edu.cn> wrote:
>
> Only add to used ring when a batch a buffer have all been used.  And if
> in order feature negotiated, add randomness to the used buffer's order,
> test the ability of vhost to reorder batched buffer.
>
> Signed-off-by: Guo Zhi <qtxuning1999@...u.edu.cn>
> ---
>  drivers/vhost/test.c | 15 ++++++++++++++-
>  1 file changed, 14 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/vhost/test.c b/drivers/vhost/test.c
> index bc8e7fb1e..1c9c40c11 100644
> --- a/drivers/vhost/test.c
> +++ b/drivers/vhost/test.c
> @@ -43,6 +43,9 @@ struct vhost_test {
>  static void handle_vq(struct vhost_test *n)
>  {
>         struct vhost_virtqueue *vq = &n->vqs[VHOST_TEST_VQ];
> +       struct vring_used_elem *heads = kmalloc(sizeof(*heads)
> +                       * vq->num, GFP_KERNEL);
> +       int batch_idx = 0;
>         unsigned out, in;
>         int head;
>         size_t len, total_len = 0;
> @@ -84,11 +87,21 @@ static void handle_vq(struct vhost_test *n)
>                         vq_err(vq, "Unexpected 0 len for TX\n");
>                         break;
>                 }
> -               vhost_add_used_and_signal(&n->dev, vq, head, 0);
> +               heads[batch_idx].id = cpu_to_vhost32(vq, head);
> +               heads[batch_idx++].len = cpu_to_vhost32(vq, len);
>                 total_len += len;
>                 if (unlikely(vhost_exceeds_weight(vq, 0, total_len)))
>                         break;
>         }
> +       if (batch_idx) {
> +               if (vhost_has_feature(vq, VIRTIO_F_IN_ORDER) && batch_idx >= 2) {

Maybe to add a module parameter to test this? Instead of trusting in
feature negotiation, "unorder_used=1" or something like that.

vhost.c:vhost_add_used_and_signal_n should support receiving buffers
in order or out of order whether F_IN_ORDER is negotiated or not.

Thanks!

> +                       vhost_add_used_and_signal_n(&n->dev, vq, &heads[batch_idx / 2],
> +                                                   batch_idx - batch_idx / 2);
> +                       vhost_add_used_and_signal_n(&n->dev, vq, heads, batch_idx / 2);
> +               } else {
> +                       vhost_add_used_and_signal_n(&n->dev, vq, heads, batch_idx);
> +               }
> +       }
>
>         mutex_unlock(&vq->mutex);
>  }
> --
> 2.17.1
>