lisa.tests.scheduler.load_tracking: Deprioritize system highpri wq wo…

Created by: deggeman

…rkers

To let the RqInvariance:test_load_correctness load-tracking test pass the task priority of the system highpri wq workers 'kworker/X:YH-/+xx' has to be lowered from 100 (nice=-20, weight=88761) to 120 (nice=0, weight=1024). (See sched_prio_to_weight[40] in kernel/sched/core.c)

Otherwise the cfs_rq load_avg contribution from these tasks is too high since our tests assume nice=0 task weight.

The issue was introduced into the Linux kernel in v5.17 by commit ba70aca0b167 ("random: defer fast pool mixing to worker"). add_interrupt_randomness() now queues system_highpri_wq workqueue items and these are running in 'kworker/X:YH-/+xx' task context.

It was first visible on Arm32 TC2 with its timer interrupt but can be seen on other platforms/interrupts as well.

Signed-off-by: Dietmar Eggemann dietmar.eggemann@arm.com