Re: [PATCH 2/5] cgroup/cpuset: Add new cpus.partition type with no load balancing

Waiman Long
2021-06-10T19:16:35Z

On 6/10/21 2:50 PM, Peter Zijlstra wrote:
> On Thu, Jun 03, 2021 at 05:24:13PM -0400, 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
>> "root-nolb" is added which allows the creation of a cpuset partition with
>> no load balancing. This will allow system administrators to dynamically
>> adjust the size of the no load balancing partition to the current need
>> of the workload without rebooting the system.
> I'm confused, why do you need this? Just create a parition for each cpu.
>
From a management point of view, it is more cumbersome to do one cpu
per partition. I have suggested this idea of 1 cpu per partition to the
container developers, but they don't seem to like it.

Cheers,
Longman