Lets start with a simple setup. Multi-node DDP in pytorch
Hi ExcitedFish86
Good question, how do you "connect" the 3 nodes? (i.e. what the framework you are using)
The problem is not really for the agents to wait (this is easily solved by additional high priority queue) the problem is will you have a "free" agent... you see my point ?
available agent, i.e. not running anything else.
I mean how long would instance 1 wait until instance 2 of the experiment is up and running?
In other words what happens of all the nodes/agents are working and we still "need" additional instance.
This is basically like "pre-allocating" the nodes, only they wait in real-time until the additional node joins them.
Agent A pulls the 3 node Task, the Task clones itself (Task B) and enqueues on "very high priory queue" Task A wait until Task B is running. Agent B picks Task B and starts running Task A "talks" to Task BThis is the equivalent of "allocating 2 agents" (basically you have to preserve one and wait for the other to be available).
BTW: Is nvcc multi Node or multi GPU ? (I thought it is a single node multi-gpu)
I see what you mean. So in a simple "all-or-nothing" solution I have to choose between potentially starving either the single node tasks (high priority + wait) or multi-node tasks (wait for a time when there are enough available agents and only then allocate the resource).
I actually meant NCCL. nvcc is the CUDA compiler 😅
NCCL communication can be both inter- and intra- node
So in theory you can clone yourself 2 extra times and push into an execution queue, but the issue might be actually making sure the resources are available. what did you have in mind?
I thought of some sort of gang-scheduling scheme should be implemented on top of the job.
Maybe the agents should somehow go through a barrier with a counter and wait there until enough agents arrived
pytorch DDP
with what backend ? gloo ? nvcc ? openmpi ?
So in a simple "all-or-nothing"
Actually this is the only solution unless preemption is supported, i.e. abort running Task to free-up an agent...
There is no "magic" solution for complex multi-node scheduling, even SLURM will essentially do the same ...
not really... what do you mean by "free" agent?