Re: [PATCH net-next v5 4/5] mvpp2: recycle buffers

From: "Russell King (Oracle)" <linux@armlinux.org.uk>
To: Matteo Croce <mcroce@linux.microsoft.com>
Cc: netdev@vger.kernel.org, linux-mm@kvack.org,
	Ayush Sawal <ayush.sawal@chelsio.com>,
	Vinay Kumar Yadav <vinay.yadav@chelsio.com>,
	Rohit Maheshwari <rohitm@chelsio.com>,
	"David S. Miller" <davem@davemloft.net>,
	Jakub Kicinski <kuba@kernel.org>,
	Thomas Petazzoni <thomas.petazzoni@bootlin.com>,
	Marcin Wojtas <mw@semihalf.com>,
	Mirko Lindner <mlindner@marvell.com>,
	Stephen Hemminger <stephen@networkplumber.org>,
	Tariq Toukan <tariqt@nvidia.com>,
	Jesper Dangaard Brouer <hawk@kernel.org>,
	Ilias Apalodimas <ilias.apalodimas@linaro.org>,
	Alexei Starovoitov <ast@kernel.org>,
	Daniel Borkmann <daniel@iogearbox.net>,
	John Fastabend <john.fastabend@gmail.com>,
	Boris Pismenny <borisp@nvidia.com>, Arnd Bergmann <arnd@arndb.de>,
	Andrew Morton <akpm@linux-foundation.org>,
	"Peter Zijlstra (Intel)" <peterz@infradead.org>,
	Vlastimil Babka <vbabka@suse.cz>, Yu Zhao <yuzhao@google.com>,
	Will Deacon <will@kernel.org>, Fenghua Yu <fenghua.yu@intel.com>,
	Roman Gushchin <guro@fb.com>, Hugh Dickins <hughd@google.com>,
	Peter Xu <peterx@redhat.com>, Jason Gunthorpe <jgg@ziepe.ca>,
	Jonathan Lemon <jonathan.lemon@gmail.com>,
	Alexander Lobakin <alobakin@pm.me>,
	Cong Wang <cong.wang@bytedance.com>, wenxu <wenxu@ucloud.cn>,
	Kevin Hao <haokexin@gmail.com>,
	Jakub Sitnicki <jakub@cloudflare.com>,
	Marco Elver <elver@google.com>,
	Willem de Bruijn <willemb@google.com>,
	Miaohe Lin <linmiaohe@huawei.com>,
	Yunsheng Lin <linyunsheng@huawei.com>,
	Guillaume Nault <gnault@redhat.com>,
	linux-kernel@vger.kernel.org, linux-rdma@vger.kernel.org,
	bpf@vger.kernel.org, Matthew Wilcox <willy@infradead.org>,
	Eric Dumazet <edumazet@google.com>,
	David Ahern <dsahern@gmail.com>,
	Lorenzo Bianconi <lorenzo@kernel.org>,
	Saeed Mahameed <saeedm@nvidia.com>, Andrew Lunn <andrew@lunn.ch>,
	Paolo Abeni <pabeni@redhat.com>,
	Sven Auhagen <sven.auhagen@voleatech.de>
Subject: Re: [PATCH net-next v5 4/5] mvpp2: recycle buffers
Date: Thu, 13 May 2021 19:20:48 +0100	[thread overview]
Message-ID: <20210513182048.GA12395@shell.armlinux.org.uk> (raw)
In-Reply-To: <20210513165846.23722-5-mcroce@linux.microsoft.com>

On Thu, May 13, 2021 at 06:58:45PM +0200, Matteo Croce wrote:
> diff --git a/drivers/net/ethernet/marvell/mvpp2/mvpp2_main.c b/drivers/net/ethernet/marvell/mvpp2/mvpp2_main.c
> index b2259bf1d299..9dceabece56c 100644
> --- a/drivers/net/ethernet/marvell/mvpp2/mvpp2_main.c
> +++ b/drivers/net/ethernet/marvell/mvpp2/mvpp2_main.c
> @@ -3847,6 +3847,7 @@ static int mvpp2_rx(struct mvpp2_port *port, struct napi_struct *napi,
>  	struct mvpp2_pcpu_stats ps = {};
>  	enum dma_data_direction dma_dir;
>  	struct bpf_prog *xdp_prog;
> +	struct xdp_rxq_info *rxqi;
>  	struct xdp_buff xdp;
>  	int rx_received;
>  	int rx_done = 0;
> @@ -3912,15 +3913,15 @@ static int mvpp2_rx(struct mvpp2_port *port, struct napi_struct *napi,
>  		else
>  			frag_size = bm_pool->frag_size;
>  
> +		if (bm_pool->pkt_size == MVPP2_BM_SHORT_PKT_SIZE)
> +			rxqi = &rxq->xdp_rxq_short;
> +		else
> +			rxqi = &rxq->xdp_rxq_long;
>  
> +		if (xdp_prog) {
> +			xdp.rxq = rxqi;
>  
> +			xdp_init_buff(&xdp, PAGE_SIZE, rxqi);
>  			xdp_prepare_buff(&xdp, data,
>  					 MVPP2_MH_SIZE + MVPP2_SKB_HEADROOM,
>  					 rx_bytes, false);
> @@ -3964,7 +3965,7 @@ static int mvpp2_rx(struct mvpp2_port *port, struct napi_struct *napi,
>  		}
>  
>  		if (pp)
> +			skb_mark_for_recycle(skb, virt_to_page(data), pp);
>  		else
>  			dma_unmap_single_attrs(dev->dev.parent, dma_addr,
>  					       bm_pool->buf_size, DMA_FROM_DEVICE,

Looking at the above, which I've only quoted the _resulting_ code after
your patch above, I don't see why you have moved the
"bm_pool->pkt_size == MVPP2_BM_SHORT_PKT_SIZE" conditional outside of
the test for xdp_prog - I don't see rxqi being used except within that
conditional. Please can you explain the reasoning there?

Thanks.

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