Re: [PATCH net-next 3/3] net: ethernet: ti: cpsw: add XDP support

[Ivan Khoronzhuk]

On Wed, May 29, 2019 at 10:16:59AM +0200, Jesper Dangaard Brouer wrote:
> On Thu, 23 May 2019 21:20:35 +0300
> Ivan Khoronzhuk <ivan.khoronzhuk@xxxxxxxxxx> wrote:
>
> > +static struct page *cpsw_alloc_page(struct cpsw_common *cpsw)
> > +{
> > +	struct page_pool *pool = cpsw->rx_page_pool;
> > +	struct page *page, *prev_page = NULL;
> > +	int try = pool->p.pool_size << 2;
> > +	int start_free = 0, ret;
> > +
> > +	do {
> > +		page = page_pool_dev_alloc_pages(pool);
> > +		if (!page)
> > +			return NULL;
> > +
> > +		/* if netstack has page_pool recycling remove the rest */
> > +		if (page_ref_count(page) == 1)
> > +			break;
> > +
> > +		/* start free pages in use, shouldn't happen */
> > +		if (prev_page == page || start_free) {
> > +			/* dma unmap/puts page if rfcnt != 1 */
> > +			page_pool_recycle_direct(pool, page);
> > +			start_free = 1;
> > +			continue;
> > +		}
> > +
> > +		/* if refcnt > 1, page has been holding by netstack, it's pity,
> > +		 * so put it to the ring to be consumed later when fast cash is
> > +		 * empty. If ring is full then free page by recycling as above.
> > +		 */
> > +		ret = ptr_ring_produce(&pool->ring, page);
>
> This looks very wrong to me!  First of all you are manipulation
> directly with the internal pool->ring and not using the API, which
> makes this code un-maintainable.
Yes I know, it's hack, it was with assumption to be dropped once page_pool
recycling is added.

> Second this is wrong, as page_pool
> assume the in-variance that pages on the ring have refcnt==1.
Yes, but this is w/o obvious reason, seems like it can work with refcnt > 1 if
remove restriction and use >= instead of ==.

As I answered on Ilias comment, I'm going to leave version from RFC and drop
this one.

> > +		if (ret) {
> > +			page_pool_recycle_direct(pool, page);
> > +			continue;
> > +		}
> > +
> > +		if (!prev_page)
> > +			prev_page = page;
> > +	} while (try--);
> > +
> > +	return page;
> > +}
>
>
> --
> Best regards,
>  Jesper Dangaard Brouer
>  MSc.CS, Principal Kernel Engineer at Red Hat
>  LinkedIn: http://www.linkedin.com/in/brouer

--
Regards,
Ivan Khoronzhuk