[RFC PATCH v3 0/3] genirq/cpuhotplug: Adjust managed interrupts according to change of housekeeping cpumask

[Costa Shulyupin <costa.shul@redhat.com>]

The housekeeping CPU masks, set up by the "isolcpus" and "nohz_full"
boot command line options, are used at boot time to exclude selected
CPUs from running some kernel housekeeping subsystems to minimize
disturbance to latency sensitive userspace applications such as DPDK.
This options can only be changed with a reboot. This is a problem for
containerized workloads running on OpenShift/Kubernetes where a
mix of low latency and "normal" workloads can be created/destroyed
dynamically and the number of CPUs allocated to each workload is often
not known at boot time.

Theoretically, complete CPU offlining/onlining could be used for
housekeeping adjustments, but this approach is not practical.
Telco companies use Linux to run DPDK in OpenShift/Kubernetes containers.
DPDK requires isolated cpus to run real-time processes.
Kubernetes manages allocation of resources for containers.
Unfortunately Kubernetes doesn't support dynamic CPU offlining/onlining:
https://github.com/kubernetes/kubernetes/issues/67500
and is not planning to support it.
Addressing this issue at the application level appears to be even
less straightforward than addressing it at the kernel level.

This series of patches is based on series
isolation: Exclude dynamically isolated CPUs from housekeeping masks:
https://lore.kernel.org/lkml/20240821142312.236970-1-longman@redhat.com/
Its purpose is to exclude dynamically isolated CPUs from some
housekeeping masks so that subsystems that check the housekeeping masks
at run time will not use those isolated CPUs.

However, some of subsystems can use obsolete housekeeping CPU masks.
Therefore, to prevent the use of these isolated CPUs, it is necessary to
explicitly propagate changes of the housekeeping masks to all subsystems
depending on the mask.

Signed-off-by: Costa Shulyupin <costa.shul@redhat.com>

---

Changes in v3:
- Address the comments by Thomas Gleixner.

Changes in v2:
- Focus in this patch series on managed interrupts only.
- https://lore.kernel.org/lkml/20240916122044.3056787-1-costa.shul@redhat.com/

Changes in v1:
- https://lore.kernel.org/lkml/20240516190437.3545310-1-costa.shul@redhat.com/

References:
- Linux Kernel Dynamic CPU Isolation: https://pretalx.com/devconf-us-2024/talk/AZBQLE/

Costa Shulyupin (3):
  sched/isolation: Add infrastructure for dynamic CPU isolation
  DO NOT MERGE: test for managed irqs adjustment
  genirq/cpuhotplug: Adjust managed irqs according to change of
    housekeeping CPU

 block/blk-mq.c           |  19 +++++++
 include/linux/blk-mq.h   |   2 +
 include/linux/cpu.h      |   4 ++
 include/linux/irq.h      |   2 +
 kernel/cgroup/cpuset.c   |   1 +
 kernel/cpu.c             |   2 +-
 kernel/irq/cpuhotplug.c  |  99 +++++++++++++++++++++++++++++++++
 kernel/sched/isolation.c |  51 +++++++++++++++--
 tests/managed_irq.sh     | 116 +++++++++++++++++++++++++++++++++++++++
 9 files changed, 291 insertions(+), 5 deletions(-)
 create mode 100755 tests/managed_irq.sh

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2.47.0