Re: [PATCH v9 4/7] cgroup/cpuset: Add a new isolated cpus.partition type

[Peter Zijlstra]

On Sun, Dec 05, 2021 at 01:32:17PM -0500, Waiman Long wrote:
> Cpuset v1 uses the sched_load_balance control file to determine if load
> balancing should be enabled.  Cpuset v2 gets rid of sched_load_balance
> as its use may require disabling load balancing at cgroup root.
> 
> For workloads that require very low latency like DPDK, the latency
> jitters caused by periodic load balancing may exceed the desired
> latency limit.
> 
> When cpuset v2 is in use, the only way to avoid this latency cost is to
> use the "isolcpus=" kernel boot option to isolate a set of CPUs. After
> the kernel boot, however, there is no way to add or remove CPUs from
> this isolated set. For workloads that are more dynamic in nature, that
> means users have to provision enough CPUs for the worst case situation
> resulting in excess idle CPUs.
> 
> To address this issue for cpuset v2, a new cpuset.cpus.partition type
> "isolated" is added which allows the creation of a cpuset partition
> without load balancing. This will allow system administrators to
> dynamically adjust the size of isolated partition to the current need
> of the workload without rebooting the system.

you can, ofcourse, create lots of 1 cpu partitions, which is effectively
what you're doing, except there was a problem with that which you also
forgot to mention.