Dear developers, normally Slurm means by "CPU" a compute core (like in "--cpus-per-task"). Now I see the entity "core" in the option "--ntasks-per-core". The wording is a little confusing. Maybe replace "CPU" by "core" whenever possible. Thank you Ulf
http://slurm.schedmd.com/srun.html Now I am comletely confused: "For example srun -c2 --threads-per-core=1 prog may allocate two cores for the job, but if each of those cores contains two threads, the job allocation will include four CPUs. The job step allocation will then launch two threads per CPU for a total of two tasks. " As default I think ntasks=1. -c 2 : 2 CPUs(=cores) per task If each core creates 2 threads I end up with 4 threads. Not with 2 tasks, 2 threads each. Right or wrong? Thanks Ulf
Normally, a "CPU" means a hyperthread rather than a core. I tried to clarify this in a new FAQ here: https://github.com/SchedMD/slurm/commit/97f8a5016c57443ec917a16a5353421096364151 With respect to your example, --threads-per-core=1 indicates that you want to use one thread per core -c (or --cpus-per-task) = 2 indicates that you want 2 CPUs Combined the two options and you get 2 threads on different cores. If your resource allocation unit is cores, then your job would be allocated 2 full cores. If your resource allocation unit is CPUs, the job would be allocated 2 threads on different cores.
I wanted to add that if your SelectTypeParameters=CR_Core_Memory, then while a CPU is considered a thread, resources are allocated to jobs at the level of cores. CR_CPU_Memory could be used to allocate resources at the level of threads, but then two different jobs could share a core, which is normally not desirable.
Dear Moe, > With respect to your example, > --threads-per-core=1 indicates that you want to use one thread per core > -c (or --cpus-per-task) = 2 indicates that you want 2 CPUs > Combined the two options and you get 2 threads on different cores. > > If your resource allocation unit is cores, then your job would be allocated > 2 full cores. If your resource allocation unit is CPUs, the job would be > allocated 2 threads on different cores. Ok, this is how I understand it. So please change the description (citation) in srun.html accordingly -> I do not get 2 TASKS. Thank you Ulf
So in your case, srun -c2 --ntasks-per-core=1 hostname prints the hostname 4 times (i.e. 4 tasks)? I only see 2 tasks.
Perhaps you could attach your slurm.conf file. Perhaps your system is configured to allocate sockets rather than cores?
If this is still a problem, please attach your slurm.conf file and a log demonstrating the problem.
Since Tuesday, we run Slurm 2.6.6. I see no more problems anymore. Thank you Ulf
fixed in 2.6.6
