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

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Date:   Tue, 2 Aug 2022 09:45:00 +0200
From:   Stefano Garzarella <sgarzare@...hat.com>
To:     Zhi Guo <qtxuning1999@...u.edu.cn>
Cc:     Eugenio Perez Martin <eperezma@...hat.com>,
        Jason Wang <jasowang@...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 Tue, Aug 2, 2022 at 4:45 AM Zhi Guo <qtxuning1999@...u.edu.cn> wrote:
>
>
>
> 2022年7月22日 下午3:12，Eugenio Perez Martin <eperezma@...hat.com> 写道：
>
> 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!
>
> That’s a good idea, The reorder feature in vhost is a "workaround” solution for the device that can't consume buffer in order,
> If that device support in order feature, The reorder in vhost will not be used.
> So we can add a parameter in vhost_test can config in order or not in order usage for used descriptors.
> A global parameter in vhost_test.c is enough?

Maybe a module parameter is easier to use (or a sysfs file), and to
test we don't need to recompile the module every time.

In view of having a CI, it's definitely easier to set the module
parameter than to recompile it.

Thanks,
Stefano