In our testing of the virtio hardware accelerator, we found that
configuring the flags of the descriptor after addr and len,
as implemented in DPDK, seems to be more friendly to the hardware.
In our Virtio hardware implementation tests, using the default
open-source code, the hardware's bulk reads ensure performance
but correctness is compromised. If we refer to the implementation code
of DPDK, placing the flags configuration of the descriptor
after addr and len, virtio backend can function properly based on
our hardware accelerator.
I am somewhat puzzled by this. From a software process perspective,
it seems that there should be no difference whether
the flags configuration of the descriptor is before or after addr and len.
However, this is not the case according to experimental test results.
We would like to know if such a change in the configuration order
is reasonable and acceptable?
Thanks.
Signed-off-by: ni.liqiang <ni_liqiang@xxxxxxx>
Reviewed-by: jin.qi <jin.qi@xxxxxxxxxx>
Tested-by: jin.qi <jin.qi@xxxxxxxxxx>
Cc: ni.liqiang <ni.liqiang@xxxxxxxxxx>
---
drivers/virtio/virtio_ring.c | 9 +++++----
1 file changed, 5 insertions(+), 4 deletions(-)
diff --git a/drivers/virtio/virtio_ring.c b/drivers/virtio/virtio_ring.c
index 6f7e5010a673..bea2c2fb084e 100644
--- a/drivers/virtio/virtio_ring.c
+++ b/drivers/virtio/virtio_ring.c
@@ -1472,15 +1472,16 @@ static inline int virtqueue_add_packed(struct virtqueue *_vq,
flags = cpu_to_le16(vq->packed.avail_used_flags |
(++c == total_sg ? 0 : VRING_DESC_F_NEXT) |
(n < out_sgs ? 0 : VRING_DESC_F_WRITE));
- if (i == head)
- head_flags = flags;
- else
- desc[i].flags = flags;
desc[i].addr = cpu_to_le64(addr);
desc[i].len = cpu_to_le32(sg->length);
desc[i].id = cpu_to_le16(id);
+ if (i == head)
+ head_flags = flags;
+ else
+ desc[i].flags = flags;
+
if (unlikely(vq->use_dma_api)) {
vq->packed.desc_extra[curr].addr = addr;
vq->packed.desc_extra[curr].len = sg->length;
--
2.34.1
