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

2022年7月22日 下午3:12，Eugenio Perez Martin [off-list ref] 写道：

On Thu, Jul 21, 2022 at 10:44 AM Guo Zhi [off-list ref] 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 <redacted>
---
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?