If you specify no cores or threads for a given job, you should end up with 1 task per node, and 1 cpu per task (see the sections for ntasks, ntasks-per-node, and cpus-per-task at [1] and [2]).
And yes, if you have one or more 10-core systems, and submit 8 1-core jobs, they’ll default to running on the same node, assuming everything was idle to start with. Though I suppose you could tell Slurm that you have 8-core nodes instead of 10-core nodes, why would you want to limit the number of jobs or tasks that run on a compute node? Most (if not all) of us let jobs run on every available core in the system (which normally means each job reserves resources for a period of time, and doesn’t try to run outside those limits), while reserving a small amount of RAM for OS and other processes. I’m not saying you can’t have a good reason for what you’re asking, but I suspect there’s a better solution than restricting how many jobs can run on a given node. [1] https://slurm.schedmd.com/sbatch.html [2] https://slurm.schedmd.com/srun.html > On Jan 28, 2020, at 10:19 PM, zz <anand6...@gmail.com> wrote: > > Hi Michael, > > Thanks for quick response what if we submit multiple job with out specifying > core or thread in the same, all jobs will run parallely depends on the cpu > available in the node, when no resouce available the job will go to queue as > pending job. if i have 10 cpu in the system, if i submit 8 jobs (that each > job requore 1 cpu max ) simultanously all 8 will run in the single node. Is > there any way to limit the number of such jobs per node? ie: even the resouce > availble can we say the node will only accept N jobs and kept all later jobs > in pending queue. (like maxjobs, but per node not on cluster level), only > cgroups is the solution I suppose. > > On Tue, Jan 28, 2020 at 7:42 PM Renfro, Michael <ren...@tntech.edu> wrote: > For the first question: you should be able to define each node’s core count, > hyperthreading, or other details in slurm.conf. That would allow Slurm to > schedule (well-behaved) tasks to each node without anything getting > overloaded. > > For the second question about jobs that aren’t well-behaved (a job requesting > 1 CPU, but starting multiple parallel threads, or multiple MPI processes), > you’ll also want to set up cgroups to constrain each job’s processes to its > share of the node (so a 1-core job starting N threads will end up with each > thread getting a 1/N share of a CPU). > >> On Jan 28, 2020, at 6:12 AM, zz <anand6...@gmail.com> wrote: >> >> Hi, >> >> I am testing slurm for a small cluster, I just want to know that is there >> anyway I could set a max job limit per node, I have nodes with different >> specs running under same qos. Please ignore if it is a stupid question. >> >> Also I would like to know what will happen when a process which is running >> on a dual core system which requires say 4 cores at some step. >> >> Thanks
