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SubjectRe: [PATCH v3 2/4] virtio_test: use random length scatterlists to test descriptor chain
On Sat, Jul 9, 2022 at 4:28 AM Guo Zhi <qtxuning1999@sjtu.edu.cn> 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@sjtu.edu.cn>
> ---
> 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
>

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