On Thu, May 31, 2018 at 09:54:27AM -0400, Waiman Long wrote: > On 05/31/2018 08:26 AM, Peter Zijlstra wrote: > > I still find all that a bit weird. > > > > So load_balance=0 basically changes a partition into a > > 'fully-partitioned partition' with the seemingly random side-effect that > > now sub-partitions are allowed to consume all CPUs. > > Are you suggesting that we should allow sub-partition to consume all the > CPUs no matter the load balance state? I can live with that if you think > it is more logical. I'm on the fence myself; the only thing I'm fairly sure of is that tying this particular behaviour to the load-balance knob seems off. > > The rationale, only given in the Changelog above, seems to be to allow > > 'easy' emulation of isolcpus. > > > > I'm still not convinced this is a useful knob to have. You can do > > fully-partitioned by simply creating a lot of 1 cpu parititions. > > That is certainly true. However, I think there are some additional > overhead in the scheduler side in maintaining those 1-cpu partitions. Right? cpuset-controller as such doesn't have much overhead scheduler wise, cpu-controller OTOH does, and there depth is the predominant factor, so many sibling groups should not matter there either. > > So this one knob does two separate things, both of which seem, to me, > > redundant. > > > > Can we please get better rationale for this? > > I am fine getting rid of the load_balance flag if this is the consensus. > However, we do need to come up with a good migration story for those > users that need the isolcpus capability. I think Mike was the one asking > for supporting isolcpus. So Mike, what is your take on that. So I don't strictly mind having a knob that does the 'fully-partitioned partition' thing -- however odd that sounds -- but I feel we should have a solid use-case for it. I also think we should not mix the 'consume all' thing with the 'fully-partitioned' thing, as they are otherwise unrelated. -- To unsubscribe from this list: send the line "unsubscribe linux-doc" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
