On 6/10/21 3:00 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.
Also, can we change isolcpus to create a default cgroup hierarchy
instead of being the fugly hack that it is? I really hate isolcpus with
a passion, it needs to die.
That is probably doable assuming that we can allow cpuset v2 to have a
non-load balanced partition.
Depending on which cpuset version is set up, we can automatically set up
a isolated subdirectory under / to contain cpus that are isolated.
However, that will be a follow-on patch after this one.
Cheers,
Longman
