On 05/10/22 09:08, Hillf Danton wrote: > On 4 Oct 2022 16:05:21 +0100 Valentin Schneider <vschneid@xxxxxxxxxx> >> It has been reported that isolated CPUs can suffer from interference due to >> per-CPU kworkers waking up just to die. >> >> A surge of workqueue activity during initial setup of a latency-sensitive >> application (refresh_vm_stats() being one of the culprits) can cause extra >> per-CPU kworkers to be spawned. Then, said latency-sensitive task can be >> running merrily on an isolated CPU only to be interrupted sometime later by >> a kworker marked for death (cf. IDLE_WORKER_TIMEOUT, 5 minutes after last >> kworker activity). >> > Is tick stopped on the isolated CPU? If tick can hit it then it can accept > more than exiting kworker. >From what I've seen in the scenarios where that happens, yes. The pool->idle_timer gets queued from an isolated CPU and ends up on a housekeeping CPU (cf. get_target_base()). > Another option is exclude isolated CPUs from > active CPUs because workqueue has other works to do than isolating CPUs. > With nohz_full on the cmdline, wq_unbound_cpumask already excludes isolated CPU, but that doesn't apply to per-CPU kworkers. Or did you mean some other mechanism? >> Prevent this by affining kworkers to the wq_unbound_cpumask (which doesn't >> contain isolated CPUs, cf. HK_TYPE_WQ) before waking them up after marking >> them with WORKER_DIE. >>
