Re: [PATCH v3 2/4] virtio_test: use random length scatterlists to test descriptor chain

[Eugenio Perez Martin]

On Sat, Jul 9, 2022 at 4:28 AM Guo Zhi <qtxuning1999@xxxxxxxxxxx> wrote:
>
> Prior implementation only use one descriptor for each io event, which
> does't test code of descriptor chain. More importantly, one descriptor
> will not use indirect feature even indirect feature is specified. Use
> random length scatterlists here to test descriptor chain.
>
> Signed-off-by: Guo Zhi <qtxuning1999@xxxxxxxxxxx>
> ---
> v3:
> - drop fda270fcd virtio_test: move magic number in code as defined constant
> ---
>  tools/virtio/virtio_test.c | 11 ++++++++---
>  1 file changed, 8 insertions(+), 3 deletions(-)
>
> diff --git a/tools/virtio/virtio_test.c b/tools/virtio/virtio_test.c
> index 95f78b311..1408a4a20 100644
> --- a/tools/virtio/virtio_test.c
> +++ b/tools/virtio/virtio_test.c
> @@ -20,6 +20,7 @@
>  #include "../../drivers/vhost/test.h"
>
>  #define RANDOM_BATCH -1
> +#define MAX_SG_FRAGS 8UL
>
>  /* Unused */
>  void *__kmalloc_fake, *__kfree_ignore_start, *__kfree_ignore_end;
> @@ -169,7 +170,8 @@ static void wait_for_interrupt(struct vdev_info *dev)
>  static void run_test(struct vdev_info *dev, struct vq_info *vq,
>                      bool delayed, int batch, int reset_n, int bufs)
>  {
> -       struct scatterlist sl;
> +       struct scatterlist sg[MAX_SG_FRAGS];
> +       int sg_size = 0;
>         long started = 0, completed = 0, next_reset = reset_n;
>         long completed_before, started_before;
>         int r, test = 1;
> @@ -194,8 +196,11 @@ static void run_test(struct vdev_info *dev, struct vq_info *vq,
>
>                         while (started < bufs &&
>                                (started - completed) < batch) {
> -                               sg_init_one(&sl, dev->buf, dev->buf_size);
> -                               r = virtqueue_add_outbuf(vq->vq, &sl, 1,
> +                               sg_size = random() % (MAX_SG_FRAGS - 1) + 1;

I'm wondering if it would be simpler to reuse batch randomness here,
and make sg_size = MIN(started - completed, MAX_SG_FRAGS). Vhost test
should go faster because the longer chains, and I guess we should hit
a good range of chain lengths with the batch tail anyway.

Thanks!

> +                               sg_init_table(sg, sg_size);
> +                               for (int i = 0; i < sg_size; ++i)
> +                                       sg_set_buf(&sg[i], dev->buf + i, 0x1);
> +                               r = virtqueue_add_outbuf(vq->vq, sg, sg_size,
>                                                          dev->buf + started,
>                                                          GFP_ATOMIC);
>                                 if (unlikely(r != 0)) {
> --
> 2.17.1
>