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 16:19:55 +0000 Message-ID: References: <81f4bbef-8d6a-d845-eb07-966bbccf4849@intel.com> 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 mga05.intel.com (mga05.intel.com [192.55.52.43]) by dpdk.org (Postfix) with ESMTP id 264A71B28B for ; Thu, 14 Feb 2019 17:19:58 +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 14-Feb-19 1:28 PM, Shahaf Shuler wrote: > Thursday, February 14, 2019 12:19 PM, Burakov, Anatoly: >> Subject: Re: [dpdk-dev] [PATCH 0/6] introduce DMA memory mapping for >> external memory >> >> 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. > > If we are going to force all to use the extmem, then there is no need w/ this API. we can have the PMDs to register when the memory is registered. > We can just drop the vfio_dma_map APIs and that's it. > Well, whether we needed it or not is not really my call, but what i can say is that using extmem_register is _necessary_ if you're going to use the PMD's. You're right, we could just map memory for DMA at register time - that would save one API call to get the memory working. It makes it a bit weird semantically, but i think we can live with that :) -- Thanks, Anatoly