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[109.173.43.194]) by smtp.gmail.com with ESMTPSA id 2adb3069b0e04-53d826a9d0asm145109e87.183.2024.11.07.01.42.25 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 07 Nov 2024 01:42:27 -0800 (PST) Date: Thu, 7 Nov 2024 12:42:25 +0300 From: Dmitry Kozlyuk <dmitry.kozliuk@gmail.com> To: "Wieckowski, Jacob" <Jacob.Wieckowski@vector.com> Cc: "users@dpdk.org" <users@dpdk.org> Subject: Re: DMA Transfers to PCIe Bar Memory Message-ID: <20241107124225.50c22ee2@sovereign> In-Reply-To: <AS4PR01MB10408FCD8A7946B6C4AFCE5C5FD5C2@AS4PR01MB10408.eurprd01.prod.exchangelabs.com> References: <AS4PR01MB10408FAF649A51468A49D9B34FD532@AS4PR01MB10408.eurprd01.prod.exchangelabs.com> <20241106204604.444529d5@sovereign> <AS4PR01MB10408FCD8A7946B6C4AFCE5C5FD5C2@AS4PR01MB10408.eurprd01.prod.exchangelabs.com> X-Mailer: Claws Mail 3.18.0 (GTK+ 2.24.33; x86_64-pc-linux-gnu) MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: quoted-printable X-BeenThere: users@dpdk.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: DPDK usage discussions <users.dpdk.org> List-Unsubscribe: <https://mails.dpdk.org/options/users>, <mailto:users-request@dpdk.org?subject=unsubscribe> List-Archive: <http://mails.dpdk.org/archives/users/> List-Post: <mailto:users@dpdk.org> List-Help: <mailto:users-request@dpdk.org?subject=help> List-Subscribe: <https://mails.dpdk.org/listinfo/users>, <mailto:users-request@dpdk.org?subject=subscribe> Errors-To: users-bounces@dpdk.org 2024-11-07 09:16 (UTC+0000), Wieckowski, Jacob: > Hi Dimitry, >=20 > thank you for the quick response. >=20 > Ok, DMA in the classic sense is not possible. > > However, if you carry out a write transfer into the BAR memory from DPDK,= then, as I understand it, this access should be divided into several small= postage-compliant TLP packets with a maximum payload size as specified in = config space.=20 >=20 > Can block transfers in sizes of 512 bytes be carried out with the rte mem= cpy? The DPDK API states that the AVX-512 memcpy parameter must be enabled = for x86 platforms. >=20 > Do other special precautions have to be taken in the DPDK environment to = setup this kind of transfer? Could you please start with the problem you're solving? DPDK uses DMA internally (mainly) to transfer packet data from/to HW. It puts physical address of the buffer, etc. to NIC queue descriptor, writes to a doorbell register, then the NIC DMA-writes/reads the buffer; PCI transfer sizes are probably selected by HW. All of this is within PMD (userspace drivers), no API is exposed. rte_memcpy() is intended for copy from RAM to RAM. You can Cc: Morten Br=C3=B8rup <mb@smartsharesystems.com> probably, but I doubt that rte_memcpy() is specialized for DMA in any way. The buffer may be filled with rte_mempcy() by application, but this is done before handling the buffer to PMD, and thus before DMA. Are you looking for functionality of "dmadev" library? https://doc.dpdk.org/guides/prog_guide/dmadev.html