From mboxrd@z Thu Jan 1 00:00:00 1970 From: "Burakov, Anatoly" Subject: Re: [PATCH 0/6] introduce DMA memory mapping for external memory Date: Thu, 14 Feb 2019 10:19:03 +0000 Message-ID: <81f4bbef-8d6a-d845-eb07-966bbccf4849@intel.com> References: Mime-Version: 1.0 Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: 8bit Cc: Yongseok Koh , Thomas Monjalon , Ferruh Yigit , "nhorman@tuxdriver.com" , Gaetan Rivet , dev To: Shahaf Shuler , Alejandro Lucero Return-path: Received: from mga09.intel.com (mga09.intel.com [134.134.136.24]) by dpdk.org (Postfix) with ESMTP id 2430B1B1E6 for ; Thu, 14 Feb 2019 11:19:06 +0100 (CET) In-Reply-To: Content-Language: en-US List-Id: DPDK patches and discussions List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: dev-bounces@dpdk.org Sender: "dev" On 13-Feb-19 7:24 PM, Shahaf Shuler wrote: > Wednesday, February 13, 2019 1:43 PM, Alejandro Lucero: >> Subject: Re: [dpdk-dev] [PATCH 0/6] introduce DMA memory mapping for >> external memory >> >> On Wed, Feb 13, 2019 at 9:11 AM Shahaf Shuler >> wrote: >> >>> This series is in continue to RFC[1]. >>> >>> The DPDK APIs expose 3 different modes to work with memory used for >> DMA: >>> >>> 1. Use the DPDK owned memory (backed by the DPDK provided >> hugepages). >>> This memory is allocated by the DPDK libraries, included in the DPDK >>> memory system (memseg lists) and automatically DMA mapped by the >> DPDK >>> layers. >>> >>> 2. Use memory allocated by the user and register to the DPDK memory >>> systems. This is also referred as external memory. Upon registration >>> of the external memory, the DPDK layers will DMA map it to all needed >>> devices. >>> >>> 3. Use memory allocated by the user and not registered to the DPDK >>> memory system. This is for users who wants to have tight control on >>> this memory. The user will need to explicitly call DMA map function in >>> order to register such memory to the different devices. >>> >>> The scope of the patch focus on #3 above. >>> >>> >> Why can not we have case 2 covering case 3? > > Because it is not our choice rather the DPDK application. > We could not allow it, and force the application to register their external memory to the DPDK memory management system. However IMO it will be wrong. > The use case exists - some application wants to manage their memory by themselves. w/o the extra overhead of rte_malloc, without creating a special socket to populate the memory and without redundant API calls to rte_extmem_*. > > Simply allocate chunk of memory, DMA map it to device and that’s it. Just a small note: while this sounds good on paper, i should point out that at least *registering* the memory with DPDK is a necessity. You may see rte_extmem_* calls as redundant (and i agree, to an extent), but we don't advertise our PMD's capabilities in a way that makes it easy to determine whether a particular PMD will or will not work without registering external memory within DPDK (i.e. does it use rte_virt2memseg() internally, for example). So, extmem register calls are a necessary evil in such case, and IMO should be called out as required for such external memory usage scenario. -- Thanks, Anatoly