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.