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Message-ID: <20250905085801.98754-1-marco.crivellari@suse.com>
Date: Fri, 5 Sep 2025 10:57:58 +0200
From: Marco Crivellari <marco.crivellari@...e.com>
To: linux-kernel@...r.kernel.org
Cc: Tejun Heo <tj@...nel.org>,
Lai Jiangshan <jiangshanlai@...il.com>,
Frederic Weisbecker <frederic@...nel.org>,
Sebastian Andrzej Siewior <bigeasy@...utronix.de>,
Marco Crivellari <marco.crivellari@...e.com>,
Michal Hocko <mhocko@...e.com>,
Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
Jakub Kicinski <kuba@...nel.org>,
Alex Deucher <alexander.deucher@....com>
Subject: [PATCH 0/3] drivers: replace wq users and add WQ_PERCPU to alloc_workqueue() users
Hi!
Below is a summary of a discussion about the Workqueue API and cpu isolation
considerations. Details and more information are available here:
"workqueue: Always use wq_select_unbound_cpu() for WORK_CPU_UNBOUND."
https://lore.kernel.org/all/20250221112003.1dSuoGyc@linutronix.de/
=== 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 consistentcy cannot be addressed without refactoring the API.
=== Plan and future plans ===
This patchset is the first stone on a refactoring needed in order to
address the points aforementioned; it will have a positive impact also
on the cpu isolation, in the long term, moving away percpu workqueue in
favor to an unbound model.
These are the main steps:
1) API refactoring (that this patch is introducing)
- Make more clear and uniform the system wq names, both per-cpu and
unbound. This to avoid any possible confusion on what should be
used.
- Introduction of WQ_PERCPU: this flag is the complement of WQ_UNBOUND,
introduced in this patchset and used on all the callers that are not
currently using WQ_UNBOUND.
WQ_UNBOUND will be removed in a future release cycle.
Most users don't need to be per-cpu, because they don't have
locality requirements, because of that, a next future step will be
make "unbound" the default behavior.
2) Check who really needs to be per-cpu
- Remove the WQ_PERCPU flag when is not strictly required.
3) Add a new API (prefer local cpu)
- There are users that don't require a local execution, like mentioned
above; despite that, local execution yeld to performance gain.
This new API will prefer the local execution, without requiring it.
=== Introduced Changes by this series ===
1) [P 1-2] Replace use 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 renamed in system_percpu_wq, and
system_unbound_wq has been renamed in system_dfl_wq.
2) [P 3] add WQ_PERCPU to remaining alloc_workqueue() users
Every alloc_workqueue() caller should use one among WQ_PERCPU or
WQ_UNBOUND. This is actually enforced warning if both or none of them
are present at the same time.
WQ_UNBOUND will be removed in a next release cycle.
=== For Maintainers ===
There are prerequisites for this series, already merged in the master branch.
The commits are:
128ea9f6ccfb6960293ae4212f4f97165e42222d ("workqueue: Add system_percpu_wq and
system_dfl_wq")
930c2ea566aff59e962c50b2421d5fcc3b98b8be ("workqueue: Add new WQ_PERCPU flag")
Thanks!
Marco Crivellari (3):
drivers: replace use of system_unbound_wq with system_dfl_wq
drivers: replace use of system_wq with system_percpu_wq
drivers: WQ_PERCPU added to alloc_workqueue users
drivers/accel/ivpu/ivpu_hw_btrs.c | 2 +-
drivers/accel/ivpu/ivpu_ipc.c | 2 +-
drivers/accel/ivpu/ivpu_job.c | 2 +-
drivers/accel/ivpu/ivpu_mmu.c | 2 +-
drivers/accel/ivpu/ivpu_pm.c | 4 +--
drivers/acpi/ec.c | 3 +-
drivers/acpi/osl.c | 6 ++--
drivers/acpi/scan.c | 2 +-
drivers/acpi/thermal.c | 3 +-
drivers/ata/libata-sff.c | 3 +-
drivers/base/core.c | 2 +-
drivers/base/dd.c | 2 +-
drivers/base/devcoredump.c | 2 +-
drivers/bus/mhi/ep/main.c | 2 +-
drivers/char/random.c | 8 ++---
drivers/char/tpm/tpm-dev-common.c | 3 +-
drivers/char/xillybus/xillybus_core.c | 2 +-
drivers/char/xillybus/xillyusb.c | 4 +--
drivers/cpufreq/tegra194-cpufreq.c | 3 +-
drivers/crypto/atmel-i2c.c | 2 +-
drivers/crypto/cavium/nitrox/nitrox_mbx.c | 2 +-
drivers/crypto/intel/qat/qat_common/adf_aer.c | 4 +--
drivers/crypto/intel/qat/qat_common/adf_isr.c | 3 +-
.../crypto/intel/qat/qat_common/adf_sriov.c | 3 +-
.../crypto/intel/qat/qat_common/adf_vf_isr.c | 3 +-
drivers/cxl/pci.c | 2 +-
drivers/extcon/extcon-intel-int3496.c | 4 +--
drivers/firewire/core-transaction.c | 3 +-
drivers/firewire/ohci.c | 3 +-
drivers/gpio/gpiolib-cdev.c | 4 +--
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/bridge/analogix/anx7625.c | 3 +-
drivers/gpu/drm/bridge/ite-it6505.c | 2 +-
drivers/gpu/drm/bridge/ti-tfp410.c | 2 +-
drivers/gpu/drm/drm_atomic_helper.c | 6 ++--
drivers/gpu/drm/drm_probe_helper.c | 2 +-
drivers/gpu/drm/drm_self_refresh_helper.c | 2 +-
drivers/gpu/drm/exynos/exynos_hdmi.c | 2 +-
.../drm/i915/display/intel_display_driver.c | 3 +-
.../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 +--
.../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 +-
.../gpu/drm/i915/selftests/i915_sw_fence.c | 2 +-
.../gpu/drm/i915/selftests/mock_gem_device.c | 2 +-
drivers/gpu/drm/nouveau/dispnv50/disp.c | 2 +-
drivers/gpu/drm/nouveau/nouveau_drm.c | 2 +-
drivers/gpu/drm/nouveau/nouveau_sched.c | 3 +-
drivers/gpu/drm/radeon/radeon_display.c | 3 +-
.../gpu/drm/rockchip/dw_hdmi_qp-rockchip.c | 4 +--
drivers/gpu/drm/rockchip/rockchip_drm_vop.c | 2 +-
drivers/gpu/drm/scheduler/sched_main.c | 2 +-
drivers/gpu/drm/tilcdc/tilcdc_crtc.c | 2 +-
drivers/gpu/drm/vc4/vc4_hdmi.c | 4 +--
drivers/gpu/drm/xe/xe_devcoredump.c | 2 +-
drivers/gpu/drm/xe/xe_device.c | 4 +--
drivers/gpu/drm/xe/xe_execlist.c | 2 +-
drivers/gpu/drm/xe/xe_ggtt.c | 2 +-
drivers/gpu/drm/xe/xe_gt_tlb_invalidation.c | 6 ++--
drivers/gpu/drm/xe/xe_guc_ct.c | 4 +--
drivers/gpu/drm/xe/xe_hw_engine_group.c | 3 +-
drivers/gpu/drm/xe/xe_oa.c | 2 +-
drivers/gpu/drm/xe/xe_pt.c | 2 +-
drivers/gpu/drm/xe/xe_sriov.c | 2 +-
drivers/gpu/drm/xe/xe_vm.c | 4 +--
drivers/greybus/operation.c | 2 +-
drivers/hid/hid-nintendo.c | 3 +-
drivers/hte/hte.c | 2 +-
drivers/hv/mshv_eventfd.c | 2 +-
drivers/i3c/master.c | 2 +-
drivers/iio/adc/pac1934.c | 2 +-
drivers/infiniband/core/cm.c | 2 +-
drivers/infiniband/core/device.c | 4 +--
drivers/infiniband/core/ucma.c | 2 +-
drivers/infiniband/hw/hfi1/init.c | 3 +-
drivers/infiniband/hw/hfi1/opfn.c | 3 +-
drivers/infiniband/hw/mlx4/cm.c | 2 +-
drivers/infiniband/hw/mlx5/odp.c | 4 +--
drivers/infiniband/sw/rdmavt/cq.c | 3 +-
drivers/infiniband/ulp/iser/iscsi_iser.c | 2 +-
drivers/infiniband/ulp/isert/ib_isert.c | 2 +-
drivers/infiniband/ulp/rtrs/rtrs-clt.c | 2 +-
drivers/infiniband/ulp/rtrs/rtrs-srv.c | 2 +-
drivers/input/keyboard/gpio_keys.c | 2 +-
drivers/input/misc/palmas-pwrbutton.c | 2 +-
drivers/input/mouse/psmouse-smbus.c | 2 +-
drivers/input/mouse/synaptics_i2c.c | 8 ++---
drivers/isdn/capi/kcapi.c | 2 +-
drivers/leds/trigger/ledtrig-input-events.c | 2 +-
drivers/md/bcache/btree.c | 3 +-
drivers/md/bcache/super.c | 30 ++++++++++---------
drivers/md/bcache/writeback.c | 2 +-
drivers/md/dm-bufio.c | 3 +-
drivers/md/dm-cache-target.c | 3 +-
drivers/md/dm-clone-target.c | 3 +-
drivers/md/dm-crypt.c | 6 ++--
drivers/md/dm-delay.c | 4 ++-
drivers/md/dm-integrity.c | 15 ++++++----
drivers/md/dm-kcopyd.c | 3 +-
drivers/md/dm-log-userspace-base.c | 3 +-
drivers/md/dm-mpath.c | 5 ++--
drivers/md/dm-raid1.c | 5 ++--
drivers/md/dm-snap-persistent.c | 3 +-
drivers/md/dm-stripe.c | 2 +-
drivers/md/dm-verity-target.c | 4 ++-
drivers/md/dm-writecache.c | 3 +-
drivers/md/dm.c | 3 +-
drivers/md/md.c | 4 +--
drivers/media/pci/ddbridge/ddbridge-core.c | 2 +-
.../platform/mediatek/mdp3/mtk-mdp3-core.c | 6 ++--
.../platform/synopsys/hdmirx/snps_hdmirx.c | 8 ++---
drivers/message/fusion/mptbase.c | 7 +++--
drivers/mmc/core/block.c | 3 +-
drivers/mmc/host/mtk-sd.c | 4 +--
drivers/mmc/host/omap.c | 2 +-
drivers/nvdimm/security.c | 4 +--
drivers/nvme/host/tcp.c | 2 ++
drivers/nvme/target/admin-cmd.c | 2 +-
drivers/nvme/target/core.c | 5 ++--
drivers/nvme/target/fabrics-cmd-auth.c | 2 +-
drivers/nvme/target/fc.c | 6 ++--
drivers/nvme/target/tcp.c | 2 +-
drivers/pci/endpoint/functions/pci-epf-mhi.c | 2 +-
drivers/pci/endpoint/functions/pci-epf-ntb.c | 5 ++--
drivers/pci/endpoint/functions/pci-epf-test.c | 3 +-
drivers/pci/endpoint/functions/pci-epf-vntb.c | 5 ++--
drivers/pci/endpoint/pci-ep-cfs.c | 2 +-
drivers/pci/hotplug/pnv_php.c | 3 +-
drivers/pci/hotplug/shpchp_core.c | 3 +-
drivers/phy/allwinner/phy-sun4i-usb.c | 14 ++++-----
.../platform/cznic/turris-omnia-mcu-gpio.c | 2 +-
.../surface/aggregator/ssh_packet_layer.c | 2 +-
.../surface/aggregator/ssh_request_layer.c | 2 +-
.../platform/surface/surface_acpi_notify.c | 2 +-
drivers/platform/x86/gpd-pocket-fan.c | 4 +--
.../x86/x86-android-tablets/vexia_atla10_ec.c | 2 +-
drivers/rapidio/rio.c | 2 +-
drivers/ras/cec.c | 2 +-
drivers/regulator/irq_helpers.c | 2 +-
drivers/regulator/qcom-labibb-regulator.c | 4 +--
drivers/scsi/be2iscsi/be_main.c | 3 +-
drivers/scsi/bnx2fc/bnx2fc_fcoe.c | 2 +-
drivers/scsi/device_handler/scsi_dh_alua.c | 2 +-
drivers/scsi/fcoe/fcoe.c | 2 +-
drivers/scsi/ibmvscsi_tgt/ibmvscsi_tgt.c | 3 +-
drivers/scsi/lpfc/lpfc_init.c | 2 +-
drivers/scsi/pm8001/pm8001_init.c | 2 +-
drivers/scsi/qedf/qedf_main.c | 15 ++++++----
drivers/scsi/qedi/qedi_main.c | 2 +-
drivers/scsi/qla2xxx/qla_os.c | 4 +--
drivers/scsi/qla2xxx/qla_target.c | 2 +-
drivers/scsi/qla2xxx/tcm_qla2xxx.c | 2 +-
drivers/scsi/qla4xxx/ql4_os.c | 3 +-
drivers/scsi/scsi_transport_fc.c | 7 +++--
drivers/scsi/scsi_transport_iscsi.c | 2 +-
drivers/soc/fsl/qbman/qman.c | 2 +-
drivers/soc/xilinx/zynqmp_power.c | 6 ++--
drivers/staging/greybus/sdio.c | 2 +-
drivers/target/sbp/sbp_target.c | 8 ++---
drivers/target/target_core_transport.c | 4 +--
drivers/target/target_core_xcopy.c | 2 +-
drivers/target/tcm_fc/tfc_conf.c | 2 +-
drivers/thunderbolt/tb.c | 2 +-
drivers/tty/serial/8250/8250_dw.c | 4 +--
drivers/tty/tty_buffer.c | 8 ++---
drivers/usb/core/hub.c | 2 +-
drivers/usb/dwc3/gadget.c | 2 +-
drivers/usb/gadget/function/f_hid.c | 3 +-
drivers/usb/host/xhci-dbgcap.c | 8 ++---
drivers/usb/host/xhci-ring.c | 2 +-
drivers/usb/storage/uas.c | 2 +-
drivers/usb/typec/anx7411.c | 3 +-
drivers/vdpa/vdpa_user/vduse_dev.c | 3 +-
drivers/virtio/virtio_balloon.c | 3 +-
drivers/xen/events/events_base.c | 6 ++--
drivers/xen/privcmd.c | 3 +-
188 files changed, 351 insertions(+), 286 deletions(-)
--
2.51.0
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