Re: [PATCH net-next RFC 3/5] vhost: introduce vhost_add_used_idx()

Willem de Bruijn
2017-09-28T00:59:53Z

>> > > @@ -199,6 +199,7 @@ int __vhost_get_vq_desc(struct vhost_virtqueue *vq,
>> > > void vhost_discard_vq_desc(struct vhost_virtqueue *, int n);
>> > > int vhost_vq_init_access(struct vhost_virtqueue *);
>> > > +int vhost_add_used_idx(struct vhost_virtqueue *vq, int n);
>> > > int vhost_add_used(struct vhost_virtqueue *, unsigned int head, int len);
>> > > int vhost_add_used_n(struct vhost_virtqueue *, struct vring_used_elem *heads,
>> > > unsigned count);
>> > Please change the API to hide the fact that there's an index that needs
>> > to be updated.
>>
>> In fact, an interesting optimization on top is just call
>> vhost_add_used_idx(vq, n) instead of n vhost_add_used_idx(vq, 1). That's the
>> reason I leave n in the API.
>>
>> Thanks
>
> Right but you could increment some internal counter in the vq
> structure then update the used index using some api
> with a generic name, e.g. add_used_complete or something like this.

That adds a layer of information hiding. If the same variable can be
kept close to the computation in a local variable and passed directly
to vhost_add_used_idx_n that is easier to follow.