On 05/31/2018 11:20 AM, Peter Zijlstra wrote: > 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 main reason for doing it this way is that I don't want to have load-balanced partition with no cpu in it. How about we just don't allow consume-all at all. Each partition must have at least 1 cpu. > >>> 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. The "consume all" and "fully-partitioned" look the same to me. Are you talking about allocating all the CPUs in a partition to sub-partitions so that there is no CPU left in the parent partition? Cheers, Longman -- 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
