So I'm trying to render in tops but it is weirdly slow.

I have 16 cores 32 threads and rendering a frame manually takes 6 seconds and uses 100% cpu for a split second.

Rendering with pdg takes atleast 4 times as long i dont understand why or what i should change.

I've been playing around with PDG too. I found that with some tasks, PDG would behave as you described. In those cases, manually setting the “Slots per work item” on the Job Parms tab in Local Scheduler to a portion of my thread count (8 in my case, which made for 6 work items at a time on my 48 cores) would get the task to complete at the speed I expected. I'm afraid I can't explain why that is, but might work for you too.

For me, it seems to happen most often with nodes that do not take advantage of 100% CPU when I run them manually. I haven't had the issue yet with the Mantra, though.

What version and what license are you using?