[PATCH v3 0/3] replace old wq(s), add WQ_PERCPU to alloc_workqueue

[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 of that, system_wq has been replaced with system_percpu_wq, and
    system_unbound_wq has been replaced with system_dfl_wq.

2) [P 3] 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 3:
- Improved commit logs

Changes in v2:
- fix typo in patch subject (add instead of added).

- in every patch is also present the specific commit hash about the
  workqueue API change.

- fixed commit log of P1 (removed "Adding system_dfl_wq...").

- P2: subject changed reflecting the effective change.

- rebased to v6.18-rc4.


Marco Crivellari (3):
  drm/i915: replace use of system_unbound_wq with system_dfl_wq
  drm/i915: replace use of system_wq with system_percpu_wq in the
    documentation
  drm/i915: add WQ_PERCPU to alloc_workqueue users

 drivers/gpu/drm/i915/display/intel_display_driver.c | 4 ++--
 drivers/gpu/drm/i915/display/intel_display_power.c  | 2 +-
 drivers/gpu/drm/i915/display/intel_tc.c             | 4 ++--
 drivers/gpu/drm/i915/gem/i915_gem_ttm_move.c        | 2 +-
 drivers/gpu/drm/i915/gt/uc/intel_guc.c              | 4 ++--
 drivers/gpu/drm/i915/gt/uc/intel_guc_ct.c           | 4 ++--
 drivers/gpu/drm/i915/gt/uc/intel_guc_submission.c   | 6 +++---
 drivers/gpu/drm/i915/i915_active.c                  | 2 +-
 drivers/gpu/drm/i915/i915_driver.c                  | 5 +++--
 drivers/gpu/drm/i915/i915_drv.h                     | 2 +-
 drivers/gpu/drm/i915/i915_sw_fence_work.c           | 2 +-
 drivers/gpu/drm/i915/i915_vma_resource.c            | 2 +-
 drivers/gpu/drm/i915/pxp/intel_pxp.c                | 2 +-
 drivers/gpu/drm/i915/pxp/intel_pxp_irq.c            | 2 +-
 drivers/gpu/drm/i915/selftests/i915_sw_fence.c      | 2 +-
 drivers/gpu/drm/i915/selftests/mock_gem_device.c    | 2 +-
 16 files changed, 24 insertions(+), 23 deletions(-)

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2.51.1