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    SubjectRe: [RFC 3/5] vhost_test: batch used buffer
    On Thu, Jul 21, 2022 at 10:44 AM Guo Zhi <qtxuning1999@sjtu.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@sjtu.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
    >

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