[PATCH v3 0/4] Replace old wq name and add WQ_PERCPU and WQ_UNBOUND to alloc_workqueue users

[Marco Crivellari]

Hi,

=== Current situation: problems ===

Let's consider a nohz_full system with isolated CPUs: wq_unbound_cpumask is
set to the housekeeping CPUs, for !WQ_UNBOUND the local CPU is selected.

This leads to different scenarios if a work item is scheduled on an
isolated CPU where "delay" value is 0 or greater then 0:
        schedule_delayed_work(, 0);

This will be handled by __queue_work() that will queue the work item on the
current local (isolated) CPU, while:

        schedule_delayed_work(, 1);

Will move the timer on an housekeeping CPU, and schedule the work there.

Currently if a user enqueue a work item using schedule_delayed_work() the
used wq is "system_wq" (per-cpu wq) while queue_delayed_work() use
WORK_CPU_UNBOUND (used when a cpu is not specified). The same applies to
schedule_work() that is using system_wq and queue_work(), that makes use
again of WORK_CPU_UNBOUND.

This lack of consistency cannot be addressed without refactoring the API.

=== Recent changes to the WQ API ===

The following, address the recent changes in the Workqueue API:

- commit 128ea9f6ccfb ("workqueue: Add system_percpu_wq and system_dfl_wq")
- commit 930c2ea566af ("workqueue: Add new WQ_PERCPU flag")

The old workqueues will be removed in a future release cycle.

=== Introduced Changes by this series ===

1) [P 1-2]  Replace uses of system_wq and system_unbound_wq

    system_wq is a per-CPU workqueue, but his name is not clear.
    system_unbound_wq is to be used when locality is not required.

    Because these specific workloads have no benefits from a per-cpu wq,
    both have been replaced with system_dfl_wq.

2) [P 3] WQ_UNBOUND added to alloc_workqueue (amdfk)
    This change make sure alloc_workqueue in amd/amdfkd is unbound,
    explicitly adding WQ_UNBOUND to the alloc_workqueue() user.

3) [P 4] WQ_PERCPU added to alloc_workqueue()

    This change adds a new WQ_PERCPU flag to explicitly request
    alloc_workqueue() to be per-cpu when WQ_UNBOUND has not been specified.


Thanks!

---
Changes in v3:
- improved message commits
- rebased on v6.19-rc2

Changes in v2:
- system_wq replaced with system_dfl_wq instead of system_percpu_wq, because
  a per-cpu workload is not strictly needed.

- use WQ_UNBOUND instead of WQ_PERCPU, because this workload will benefit
  from unbound work.

- commits log integrated with commits about recent Workqueue API changes.

- work rebased on v6.18-rc4


Marco Crivellari (4):
  drm/amdgpu: replace use of system_unbound_wq with system_dfl_wq
  drm/amdgpu: replace use of system_wq with system_dfl_wq
  amd/amdkfd: add WQ_UNBOUND to alloc_workqueue users
  drm/radeon: add WQ_PERCPU to alloc_workqueue users

 drivers/gpu/drm/amd/amdgpu/aldebaran.c     | 2 +-
 drivers/gpu/drm/amd/amdgpu/amdgpu_device.c | 6 +++---
 drivers/gpu/drm/amd/amdgpu/amdgpu_reset.c  | 2 +-
 drivers/gpu/drm/amd/amdkfd/kfd_process.c   | 3 ++-
 drivers/gpu/drm/radeon/radeon_display.c    | 3 ++-
 5 files changed, 9 insertions(+), 7 deletions(-)

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2.52.0