From mboxrd@z Thu Jan 1 00:00:00 1970 From: "Tan, Jianfeng" Subject: Re: [PATCH] eal: add option --avail-cores to detect lcores Date: Wed, 9 Mar 2016 22:17:28 +0800 Message-ID: <56E03078.3000501@intel.com> References: <1453661393-85704-1-git-send-email-jianfeng.tan@intel.com> <1457085957-115339-1-git-send-email-jianfeng.tan@intel.com> <56DE9359.1090705@redhat.com> <56DF0E0A.8000108@intel.com> <56E01F94.2060906@redhat.com> <56E02AC2.7010704@intel.com> <2601191342CEEE43887BDE71AB97725836B1A536@irsmsx105.ger.corp.intel.com> Mime-Version: 1.0 Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: 7bit To: "Ananyev, Konstantin" , Panu Matilainen , "dev@dpdk.org" Return-path: Received: from mga03.intel.com (mga03.intel.com [134.134.136.65]) by dpdk.org (Postfix) with ESMTP id C4FA82BC2 for ; Wed, 9 Mar 2016 15:17:54 +0100 (CET) In-Reply-To: <2601191342CEEE43887BDE71AB97725836B1A536@irsmsx105.ger.corp.intel.com> List-Id: patches and discussions about DPDK List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: dev-bounces@dpdk.org Sender: "dev" On 3/9/2016 10:01 PM, Ananyev, Konstantin wrote: > >> -----Original Message----- >> From: dev [mailto:dev-bounces@dpdk.org] On Behalf Of Tan, Jianfeng >> Sent: Wednesday, March 09, 2016 1:53 PM >> To: Panu Matilainen; dev@dpdk.org >> Subject: Re: [dpdk-dev] [PATCH] eal: add option --avail-cores to detect lcores >> >> >> >> On 3/9/2016 9:05 PM, Panu Matilainen wrote: >>> On 03/08/2016 07:38 PM, Tan, Jianfeng wrote: >>>> Hi Panu, >>>> >>>> On 3/8/2016 4:54 PM, Panu Matilainen wrote: >>>>> On 03/04/2016 12:05 PM, Jianfeng Tan wrote: >>>>>> This patch adds option, --avail-cores, to use lcores which are >>>>>> available >>>>>> by calling pthread_getaffinity_np() to narrow down detected cores >>>>>> before >>>>>> parsing coremask (-c), corelist (-l), and coremap (--lcores). >>>>>> >>>>>> Test example: >>>>>> $ taskset 0xc0000 ./examples/helloworld/build/helloworld \ >>>>>> --avail-cores -m 1024 >>>>>> >>>>>> Signed-off-by: Jianfeng Tan >>>>>> Acked-by: Neil Horman >>>>> Hmm, to me this sounds like something that should be done always so >>>>> there's no need for an option. Or if there's a chance it might do the >>>>> wrong thing in some rare circumstance then perhaps there should be a >>>>> disabler option instead? >>>> Thanks for comments. >>>> >>>> Yes, there's a use case that we cannot handle. >>>> >>>> If we make it as default, DPDK applications may fail to start, when user >>>> specifies a core in isolcpus and its parent process (say bash) has a >>>> cpuset affinity that excludes isolcpus. Originally, DPDK applications >>>> just blindly do pthread_setaffinity_np() and it always succeeds because >>>> it always has root privilege to change any cpu affinity. >>>> >>>> Now, if we do the checking in rte_eal_cpu_init(), those lcores will be >>>> flagged as undetected (in my older implementation) and leads to failure. >>>> To make it correct, we would always add "taskset mask" (or other ways) >>>> before DPDK application cmd lines. >>>> >>>> How do you think? >>> I still think it sounds like something that should be done by default >>> and maybe be overridable with some flag, rather than the other way >>> around. Another alternative might be detecting the cores always but if >>> running as root, override but with a warning. >> For your second solution, only root can setaffinity to isolcpus? >> Your first solution seems like a promising way for me. >> >>> But I dont know, just wondering. To look at it from another angle: why >>> would somebody use this new --avail-cores option and in what >>> situation, if things "just work" otherwise anyway? >> For DPDK applications, the most common case to initialize DPDK is like >> this: "$dpdk-app [options for DPDK] -- [options for app]", so users need >> to specify which cores to run and how much hugepages are used. Suppose >> we need this dpdk-app to run in a container, users already give those >> information when they build up the cgroup for it to run inside, this >> option or this patch is to make DPDK more smart to discover how much >> resource will be used. Make sense? > But then, all we need might be just a script that would extract this information from the system > and form a proper cmdline parameter for DPDK? Yes, a script will work. Or to construct (argc, argv) to call rte_eal_init() in the application. But as Neil Horman once suggested, a simple pthread_getaffinity_np() will get all things done. So if it worth a patch here? Thanks, Jianfeng > Konstantin > >> Thanks, >> Jianfeng >> >> >>> - Panu - >>>