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Tue, 11 Feb 2025 10:01:11 -0800 (PST) Message-ID: <18dc77ac-5671-43ed-ac88-1c145bc37a00@gmail.com> Date: Tue, 11 Feb 2025 20:01:08 +0200 Precedence: bulk X-Mailing-List: netdev@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH net-next 1/4] eth: mlx4: create a page pool for Rx To: Jakub Kicinski Cc: davem@davemloft.net, netdev@vger.kernel.org, edumazet@google.com, pabeni@redhat.com, andrew+netdev@lunn.ch, horms@kernel.org, tariqt@nvidia.com, hawk@kernel.org References: <20250205031213.358973-1-kuba@kernel.org> <20250205031213.358973-2-kuba@kernel.org> <76129ce2-37a7-4e97-81f6-f73f72723a17@gmail.com> <20250206150434.4aff906b@kernel.org> Content-Language: en-US From: Tariq Toukan In-Reply-To: <20250206150434.4aff906b@kernel.org> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit On 07/02/2025 1:04, Jakub Kicinski wrote: > On Thu, 6 Feb 2025 21:44:38 +0200 Tariq Toukan wrote: >>> - if (xdp_rxq_info_reg(&ring->xdp_rxq, priv->dev, queue_index, 0) < 0) >>> + pp.flags = PP_FLAG_DMA_MAP; >>> + pp.pool_size = MLX4_EN_MAX_RX_SIZE; >> >> Pool size is not accurate. >> From one side, MLX4_EN_MAX_RX_SIZE might be too big compared to the >> actual size. >> >> However, more importantly, it can be too small when working with large >> MTU. This is mutually exclusive with XDP in mlx4. >> >> Rx ring entries consist of 'frags', each entry needs between 1 to 4 >> (MLX4_EN_MAX_RX_FRAGS) frags. In default MTU, each page shared between >> two entries. > > The pool_size is just the size of the cache, how many unallocated > DMA mapped pages we can keep around before freeing them to system > memory. It has no implications for correctness. Right, it doesn't hurt correctness. But, we better have the cache size derived from the overall ring buffer size, so that the memory consumption/footprint reflects the user configuration. Something like: ring->size * (priv->frag_info[i].frag_stride for i < num_frags). or roughly ring->size * MLX4_EN_EFF_MTU(dev->mtu).