Re: [PATCH net-next 1/3] vhost: generalize adding used elem

[Jason Wang]

On 2018/12/14 äå3:41, Michael S. Tsirkin wrote:
> On Thu, Dec 13, 2018 at 06:10:20PM +0800, Jason Wang wrote:
> > 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@xxxxxxxxxx>
>
> 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


> > ---
> >   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