[slurm-users] addressing NVIDIA MIG + non MIG devices in Slurm

[Matthias Leopold]

Hi,

we have 2 DGX A100 systems which we would like to use with Slurm. We 
want to use the MIG feature for _some_ of the GPUs. As I somehow 
suspected I couldn't find a working setup for this in Slurm yet. I'll 
describe the configuration variants I tried after creating the MIG 
instances, it might be a longer read, please bear with me.

1. using slurm-mig-discovery for gres.conf 
(https://gitlab.com/nvidia/hpc/slurm-mig-discovery)
- CUDA_VISIBLE_DEVICES: list of indices
-> seems to bring a working setup and full flexibility at first, but 
when taking a closer look the selection of GPU devices is completely 
unpredictable (output of nvidia-smi inside Slurm job)

2. using "AutoDetect=nvml" in gres.conf (Slurm docs)
- CUDA_VISIBLE_DEVICES: MIG format (see 
https://docs.nvidia.com/cuda/cuda-c-programming-guide/index.html#env-vars)

2.1 converting ALL GPUs to MIG
- also a full A100 is converted to a 7g.40gb MIG instance
- gres.conf: "AutoDetect=nvml" only
- slurm.conf Node Def: naming all MIG types (read from slurmd debug log)
-> working setup
-> problem: IPC (MPI) between MIG instances not possible, this seems to 
be a by-design limitation

2.2 converting SOME GPUs to MIG
- some A100 are NOT in MIG mode

2.2.1 using "AutoDetect=nvml" only (Variant 1)
- slurm.conf Node Def: Gres with and without type
-> problem: fatal: _foreach_slurm_conf: Some gpu GRES in slurm.conf have 
a type while others do not (slurm_gres->gres_cnt_config (26) > tmp_count 
(21))

2.2.2 using "AutoDetect=nvml" only (Variant 2)
- slurm.conf Node Def: only Gres without type (sum of MIG + non MIG)
-> problem: different GPU types can't be requested

2.2.3 using partial "AutoDetect=nvml"
- gres.conf: "AutoDetect=nvml" + hardcoding of non MIG GPUs
- slurm.conf Node Def: MIG + non MIG Gres types
-> produces a "perfect" config according to slurmd debug log
-> problem: the sanity-check mode of "AutoDetect=nvml" prevents 
operation (?)
-> Reason=gres/gpu:1g.5gb count too low (0 < 21) [slurm at 2022-01-27T11:23:59]

2.2.4 using static gres.conf with NVML generated config
- using a gres.conf with NVML generated config where I can define the 
type for non MIG GPU and also set the UniqueId for MIG instances would 
be the perfect solution
- slurm.conf Node Def: MIG + non MIG Gres types
-> problem: it doesn't work
-> Parsing error at unrecognized key: UniqueId

Thanks for reading this far. Am I missing something? How can MIG and non 
MIG devices be addressed in a cluster? This setup of having MIG and non 
MIG devices can't be exotic, since having ONLY MIG devices has severe 
disadvantages (see 2.1). Thanks again for any advice.

Matthias