On Wed, 05 Nov 2025, Krzysztof Karas <[email protected]> wrote:
> Hi Marco,
>
> thanks for addressing my comments!
>
> Reviewed-by: Krzysztof Karas <[email protected]>
> on the whole series.
The series absolutely must go through both i915 and xe CI before
merging. Krzysztof, can you please make follow through with that?
BR,
Jani.
>
> Best Regards,
> Krzysztof
>
> On 2025-11-04 at 11:00:29 +0100, Marco Crivellari wrote:
>> 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(-)
>>
>> --
>> 2.51.1
>>
>
--
Jani Nikula, Intel
