Hello, Joel. On Mon, Jan 29, 2024 at 05:42:54PM -0500, Joel Fernandes wrote: > > This is a great topic. I think integrating/merging such mechanism with the NEST > > scheduler could be useful too? You mentioned there is sched_ext implementation > > of NEST already? One reason that's interesting to me is the task-packing and > > less-spreading may have power benefits, this is exactly what EAS on ARM does, > > but it also uses an energy model to know when packing is a bad idea. Since we > > don't have fine grained control of frequency on Intel, I wonder what else can we > > do to know when the scheduler should pack and when to spread. Maybe something > > simple which does not need an energy model but packs based on some other > > signal/heuristic would be great in the short term. > > > > Maybe a signal can be the "Quality of service (QoS)" approach where tasks with > > lower QoS are packed more aggressively and higher QoS are spread more (?). This was done for a different purpose (improving tail latencies on latency critical workload) but it uses soft-affinity based packing which maybe can translate to power-aware scheduling: https://github.com/sched-ext/scx/blob/case-studies/case-studies/scx_layered.md I have a raptor lake-H laptop which has E and P cores and by default the threads are being spread across all CPUs which probably isn't best for power consumption. I was thinking about writing a scheduler which uses a similar strategy as scx_layered - pack the cores one by one overflowing to the next core from E to P when the average utilization crosses a set threshold. Most of the logic is already in scx_layered, so maybe it can just be a part of that. I'm curious whether whether and how much power can be saved with a generic approach like that. Thanks. -- tejun
