> -----Original Message----- > From: Tan, Jianfeng > Sent: Wednesday, March 09, 2016 2:17 PM > To: Ananyev, Konstantin; Panu Matilainen; dev at dpdk.org > Subject: Re: [dpdk-dev] [PATCH] eal: add option --avail-cores to detect lcores > > > > On 3/9/2016 10:01 PM, Ananyev, Konstantin wrote: > > > >> -----Original Message----- > >> From: dev [mailto:dev-bounces at dpdk.org] On Behalf Of Tan, Jianfeng > >> Sent: Wednesday, March 09, 2016 1:53 PM > >> To: Panu Matilainen; dev at 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 <jianfeng.tan at intel.com> > >>>>>> Acked-by: Neil Horman <nhorman at tuxdriver.com> > >>>>> 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?
Don't know... Personally I would prefer not to put extra logic inside EAL. For me - there are too many different options already.
