by Jesper Dangaard Brouer

[permalink] [raw]

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

On Thu, 23 May 2019 21:20:35 +0300
Ivan Khoronzhuk <[email protected]> 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. Second this is wrong, as page_pool
assume the in-variance that pages on the ring have refcnt==1.

> + 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

2019-05-29 09:59:56

by Ivan Khoronzhuk

[permalink] [raw]

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

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 <[email protected]> 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