Hi Jianfeng, > -----Original Message----- > From: Tan, Jianfeng > Sent: Wednesday, March 09, 2016 2:56 PM > To: Ananyev, Konstantin; Panu Matilainen; dev at dpdk.org > Subject: Re: [dpdk-dev] [PATCH] eal: add option --avail-cores to detect lcores > > Hi Konstantin, > > On 3/9/2016 10:44 PM, Ananyev, Konstantin wrote: > > > >> -----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. > > Then how about make it default in rte_eal_cpu_init()? And it is already > known it will bring trouble to those use isolcpus users, they need to > add "taskset [mask]" before starting a DPDK app.
As I said - provide a script? Same might be for amount of hugepage memory available to the user? > > > From other side looking at the patch itself: > > You are updating lcore_count and lcore_config[],based on physical cpu > > availability, > > but these days it is not always one-to-one mapping between EAL lcore and > > physical cpu. > > Shouldn't that be taken into account? > > I have not see the problem so far, because this work is done before > parsing coremask (-c), corelist (-l), and coremap (--lcores). If a core > is disabled here, it's like it is not detected in rte_eal_cpu_init(). Or > could you please give more hints? I didn't test try changes, so probably I am missing something. Let say iuser allowed to use only cpus 0-3. If he would type with: --avail-cores --lcores='(1-7)@2', then only lcores 1-3 would be started. Again if user would specify '2@(1-7)' it would also be undetected that cpus 4-7 are note available to the user. Is that so? Konstantin > > Thanks, > Jianfeng > > > Konstantin > > > > > >
