On 2018/12/14 上午3:41, Michael S. Tsirkin wrote:

On Thu, Dec 13, 2018 at 06:10:20PM +0800, Jason Wang wrote:

quoted

Use one generic vhost_copy_to_user() instead of two dedicated
accessor. This will simplify the conversion to fine grain accessors.

Signed-off-by: Jason Wang <jasowang@redhat.com>

The reason we did it like this is because it was faster.
Want to try benchmarking before we change it?

Faster is a good side effect of such conversion. Otherwise we need two 
new fine grain memory accessor.

But, anyway, I can test its impact.

Thanks

quoted

---
  drivers/vhost/vhost.c | 11 +----------
  1 file changed, 1 insertion(+), 10 deletions(-)

diff --git a/drivers/vhost/vhost.c b/drivers/vhost/vhost.c
index 3a5f81a66d34..1c54ec1b82f8 100644
--- a/drivers/vhost/vhost.c
+++ b/drivers/vhost/vhost.c

@@ -2164,16 +2164,7 @@ static int __vhost_add_used_n(struct vhost_virtqueue *vq,
  
  	start = vq->last_used_idx & (vq->num - 1);
  	used = vq->used->ring + start;
-	if (count == 1) {
-		if (vhost_put_user(vq, heads[0].id, &used->id)) {
-			vq_err(vq, "Failed to write used id");
-			return -EFAULT;
-		}
-		if (vhost_put_user(vq, heads[0].len, &used->len)) {
-			vq_err(vq, "Failed to write used len");
-			return -EFAULT;
-		}
-	} else if (vhost_copy_to_user(vq, used, heads, count * sizeof *used)) {
+	if (vhost_copy_to_user(vq, used, heads, count * sizeof *used)) {
  		vq_err(vq, "Failed to write used");
  		return -EFAULT;
  	}

-- 
2.17.1