Affinity of managed interrupts cannot be changed even if they target isolated CPU

Solution Unverified - Updated -

Issue

  • Affinity of some interrupts cannot be changed via /proc/irq/X/... and such interrupts ignore irqaffinity kernel parameter from cmdline.
  • If such interrupts are so-called "managed" interrupts, then requests to change its affinity from userspace will not work.
  • Such "managed" interrupts can target isolated CPU cores and it will be impossible to re-target the IRQ to another CPU.

Environment

  • Red Hat Enterprise Linux 8
  • Red Hat Enterprise Linux 7 starting with kernel version 3.10.0-957.el7

The issue was not observed on Red Hat Enterprise Linux 6.

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