Received-SPF: pass (google.com: domain of linux-kernel+bounces-138713-linux.lists.archive=gmail.com@vger.kernel.org designates 139.178.88.99 as permitted sender) client-ip=139.178.88.99;
Message-ID: <9cb903df-3e83-409a-aa4b-218742804cc6@baylibre.com>
Date: Wed, 10 Apr 2024 16:02:00 +0200
Precedence: bulk
MIME-Version: 1.0
User-Agent: Mozilla Thunderbird
Subject: Re: [PATCH net-next v8 3/3] net: ethernet: ti: am65-cpsw: Add minimal
 XDP support
To: Jakub Kicinski <kuba@kernel.org>
Cc: "David S. Miller" <davem@davemloft.net>,
 Eric Dumazet <edumazet@google.com>, Paolo Abeni <pabeni@redhat.com>,
 Russell King <linux@armlinux.org.uk>, Alexei Starovoitov <ast@kernel.org>,
 Daniel Borkmann <daniel@iogearbox.net>,
 Jesper Dangaard Brouer <hawk@kernel.org>,
 John Fastabend <john.fastabend@gmail.com>,
 Sumit Semwal <sumit.semwal@linaro.org>,
 =?UTF-8?Q?Christian_K=C3=B6nig?= <christian.koenig@amd.com>,
 Simon Horman <horms@kernel.org>, Andrew Lunn <andrew@lunn.ch>,
 Ratheesh Kannoth <rkannoth@marvell.com>,
 Naveen Mamindlapalli <naveenm@marvell.com>, danishanwar@ti.com,
 yuehaibing@huawei.com, rogerq@kernel.org, netdev@vger.kernel.org,
 linux-kernel@vger.kernel.org, bpf@vger.kernel.org,
 linux-media@vger.kernel.org, dri-devel@lists.freedesktop.org,
 linaro-mm-sig@lists.linaro.org
References: <20240223-am65-cpsw-xdp-basic-v8-0-f3421b58da09@baylibre.com>
 <20240223-am65-cpsw-xdp-basic-v8-3-f3421b58da09@baylibre.com>
 <20240409174928.58a7c3f0@kernel.org>
Content-Language: en-US
From: Julien Panis <jpanis@baylibre.com>
In-Reply-To: <20240409174928.58a7c3f0@kernel.org>
Content-Type: text/plain; charset=UTF-8; format=flowed
Content-Transfer-Encoding: 7bit

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;
>> +	}