[RFC PATCH v2 06/11] page-pool: add device memory support

[Willem de Bruijn]

> > Any regression in page pool can be avoided in the common case that
> > does not use device mem by placing that behind a static_branch. Would
> > that address your performance concerns?
> >
>
> No. This will not help.
>
> The problem is that every where in the page_pool code it is getting
> polluted with:
>
>    if (page_is_page_pool_iov(page))
>      call-some-iov-func-instead()
>
> Like: the very central piece of getting the refcnt:
>
> +static inline int page_pool_page_ref_count(struct page *page)
> +{
> +       if (page_is_page_pool_iov(page))
> +               return page_pool_iov_refcount(page_to_page_pool_iov(page));
> +
> +       return page_ref_count(page);
> +}
>
>
> The fast-path of the PP is used for XDP_DROP scenarios, and is currently
> around 14 cycles (tsc). Thus, any extra code in this code patch will
> change the fast-path.

With static_branch disabled, it would only insert a NOP?