vmstat: skip periodic vmstat update for isolated CPUs

Merge Request Required Information

vmstat: skip periodic vmstat update for isolated CPUs

Bugzilla: https://bugzilla.redhat.com/show_bug.cgi?id=2118482

Commit be5e015d107d5336f298b74ea5a4f0b1773bc6f9

Testing: tested by verifying vmstat_update is not queued to isolated CPUs

Problem: The interruption caused by vmstat_update is undesirable for certain applications.

With workloads that are running on isolated cpus with nohz full mode to shield off any kernel interruption. For example, a VM running a time sensitive application with a 50us maximum acceptable interruption (use case: soft PLC).

oslat 1094.456862: sys_mlock(start: 7f7ed0000b60, len: 1000) oslat 1094.456971: workqueue_queue_work: ... function=vmstat_update ... oslat 1094.456974: sched_switch: prev_comm=oslat ... ==> next_comm=kworker/5:1 ... kworker 1094.456978: sched_switch: prev_comm=kworker/5:1 ==> next_comm=oslat ...

The example above shows an additional 7us for the oslat -> kworker -> oslat

switches. In the case of a virtualized CPU, and the vmstat_update interruption in the host (of a qemu-kvm vcpu), the latency penalty observed in the guest is higher than 50us, violating the acceptable latency threshold.

Signed-off-by: Marcelo Tosatti mtosatti@redhat.com

Summary of Changes

5116c27e vmstat: skip periodic vmstat update for isolated CPUs b38fe109 sched/isolation: add cpu_is_isolated() API 6a792697a53af5b3028aa2918b40677effbc349f memcg: do not drain charge pcp caches on remote isolated cpus

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