Re: [PATCH net-next v8 3/3] net: ethernet: ti: am65-cpsw: Add minimal XDP support

[Julien Panis <jpanis@baylibre.com>]

On 4/10/24 02:49, Jakub Kicinski wrote:
> On Mon, 08 Apr 2024 11:38:04 +0200 Julien Panis wrote:
>> +static struct sk_buff *am65_cpsw_alloc_skb(struct am65_cpsw_rx_chn *rx_chn,
>> +					   struct net_device *ndev,
>> +					   unsigned int len,
>> +					   int desc_idx,
>> +					   bool allow_direct)
>> +{
>> +	struct sk_buff *skb;
>> +	struct page *page;
>> +
>> +	page = page_pool_dev_alloc_pages(rx_chn->page_pool);
>> +	if (unlikely(!page))
>> +		return NULL;
>> +
>> +	len += AM65_CPSW_HEADROOM;
>> +
>> +	skb = build_skb(page_address(page), len);
> You shouldn't build the skb upfront any more. Give the page to the HW,
> once HW sends you a completion - build the skbs. If build fails
> (allocation failure) just give the page back to HW. If it succeeds,
> however, you'll get a skb which is far more likely to be cache hot.

Not sure I get this point.

"Give the page to the HW" = Do you mean that I should dma_map_single()
a full page (|PAGE_SIZE|) in am65_cpsw_nuss_rx_push() ?


>
>> +	if (unlikely(!skb)) {
>> +		page_pool_put_full_page(rx_chn->page_pool, page, allow_direct);
>> +		rx_chn->pages[desc_idx] = NULL;
>> +		return NULL;
>> +	}