Re: [PATCH v2 3/4] virtio_test: use random length scatterlists to test descriptor chain

[Guo Zhi]

On 2022/7/7 13:16, Michael S. Tsirkin wrote:
> On Thu, Jul 07, 2022 at 10:44:08AM +0800, Guo Zhi 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>
> > ---
> >   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 1ecd64271..363695b33 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
> >   #define ALIGN 4096
> >   #define RINGSIZE   256
> >   #define TEST_BUF_NUM 0x100000
> > @@ -172,7 +173,8 @@ 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;
> > @@ -197,8 +199,11 @@ 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;
> > +				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)) {
> random on data path is pretty expensive.
> I would suggest get an array size from user (and maybe a seed?) and
> pregenerate some numbers, then reuse.
SGTM, I will prepare a random number array before add outbuf begin.
> > --
> > 2.17.1