Yeah, to PBS a chunk is a chunk. Now of course a job requesting nodes or a job requesting ranks might have a different place spec (scatter vs free). From your current use cases, only grouping is needed at the chunk level. Will you need the scatter/free placement as well?
If the difference is between memory requests, is there a reason the normal ‘mem’ resource isn’t enough? Or is it that certain models have larger amounts of memory. You want to place just the chunks that require the larger amount of memory on those models instead of forcing all the chunks of the job to go on the larger memory models.
If the majority of your jobs will not need per-chunk grouping, then per-job grouping might work for you in a pinch. Per-job grouping can satisfy all your use cases in a sub-par way. In the use case where one chunk has grouping and the other chunk does not, PBS has freedom of where to place the second chunk. With per-job placement, it just limits that freedom to the same group as the first chunk. In the case where you have two chunks which need to be grouped on model, but the model may be different. Once again, the scheduler has the freedom of where to place each of the two chunks. With per-job placement, it is once again sub-par and limits that freedom to having both chunks on the same model.
I don’t mean that this isn’t a valuable enhancement. I’m just pointing out that you can kind of get what you want today, while you wait for us to do a better job of placing chunks in groups.
Bhroam