Hi, That was just I thought, ntasks for mpi and cpus-per-task for multithreading. So, for example, if every node has 24 cores, is there any difference between these commands?
sbatch --ntasks 24 [...] sbatch --ntasks 1 --cpus-per-task 24 [...] regards. El jue., 22 feb. 2018 a las 9:52, Loris Bennett (<loris.benn...@fu-berlin.de>) escribió: > Hi Chris, > > Christopher Samuel <ch...@csamuel.org> writes: > > > On 22/02/18 18:49, Miguel Gutiérrez Páez wrote: > > > >> What's the real meaning of ntasks? Has cpus-per-task and ntasks the > >> same meaning in sbatch and srun? > > > > --ntasks is for parallel distributed jobs, where you can run lots of > > independent processes that collaborate using some form of communication > > between the processes (usually MPI for HPC). > > > > So inside your batch script you would use "srun" to start up the tasks. > > > > However, unless you code is written to make use of that interface then > > it's not really going to help you, and so for any multithreaded > > application you need to use --cpus-per-task instead. > > [snip (11 lines)] > > But does it make any difference for a multithreaded program if I have > > #SBATCH --ntasks=4 > #SBATCH --nodes=1-1 > > rather than > > #SBATCH --ntasks=1 > #SBATCH --cpus-per-task=4 > > Up to now I have only thought of --cpus-per-task in connection with > hybrid MPI/OpenMP jobs, which we don't actually have. Thus I tend to > tell users to think always in terms of tasks, regardless of whether > these are MPI processes or just threads. > > One downside of my approach is that if the user forgets to specify > --nodes and --ntasks is greater than 1, non-MPI jobs can be assigned to > multiple nodes. > > Cheers, > > Loris > > -- > Dr. Loris Bennett (Mr.) > ZEDAT, Freie Universität Berlin Email loris.benn...@fu-berlin.de > >
