[PATCH net-next v2 0/3] net: replace wq users and add WQ_PERCPU to alloc_workqueue() users

[Marco Crivellari <marco.crivellari@suse.com>]

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.

        WQ_UNBOUND will be removed in a next release cycle.

Thanks!


---
Changes in v2:
- wireless removed from this series
- work rebased on latest net-next changes


Marco Crivellari (3):
  net: replace use of system_unbound_wq with system_dfl_wq
  net: replace use of system_wq with system_percpu_wq
  net: WQ_PERCPU added to alloc_workqueue users

 drivers/net/can/spi/hi311x.c                         |  3 ++-
 drivers/net/can/spi/mcp251x.c                        |  3 ++-
 drivers/net/ethernet/cavium/liquidio/lio_core.c      |  2 +-
 drivers/net/ethernet/cavium/liquidio/lio_main.c      |  8 +++++---
 drivers/net/ethernet/cavium/liquidio/lio_vf_main.c   |  3 ++-
 .../net/ethernet/cavium/liquidio/request_manager.c   |  2 +-
 .../net/ethernet/cavium/liquidio/response_manager.c  |  3 ++-
 drivers/net/ethernet/freescale/dpaa2/dpaa2-eth.c     |  2 +-
 .../net/ethernet/hisilicon/hns3/hns3pf/hclge_main.c  |  3 ++-
 drivers/net/ethernet/intel/fm10k/fm10k_main.c        |  2 +-
 drivers/net/ethernet/intel/i40e/i40e_main.c          |  2 +-
 drivers/net/ethernet/marvell/octeontx2/af/cgx.c      |  2 +-
 .../net/ethernet/marvell/octeontx2/af/mcs_rvu_if.c   |  2 +-
 drivers/net/ethernet/marvell/octeontx2/af/rvu_cgx.c  |  2 +-
 drivers/net/ethernet/marvell/octeontx2/af/rvu_rep.c  |  2 +-
 .../net/ethernet/marvell/octeontx2/nic/cn10k_ipsec.c |  3 ++-
 .../net/ethernet/marvell/prestera/prestera_main.c    |  2 +-
 drivers/net/ethernet/marvell/prestera/prestera_pci.c |  2 +-
 drivers/net/ethernet/mellanox/mlxsw/core.c           |  4 ++--
 drivers/net/ethernet/netronome/nfp/nfp_main.c        |  2 +-
 drivers/net/ethernet/qlogic/qed/qed_main.c           |  3 ++-
 drivers/net/ethernet/sfc/efx_channels.c              |  2 +-
 drivers/net/ethernet/sfc/siena/efx_channels.c        |  2 +-
 drivers/net/ethernet/wiznet/w5100.c                  |  2 +-
 drivers/net/fjes/fjes_main.c                         |  5 +++--
 drivers/net/macvlan.c                                |  2 +-
 drivers/net/netdevsim/dev.c                          |  6 +++---
 drivers/net/phy/sfp.c                                | 12 ++++++------
 drivers/net/wireguard/device.c                       |  6 ++++--
 drivers/net/wwan/t7xx/t7xx_hif_dpmaif_rx.c           |  3 ++-
 drivers/net/wwan/wwan_hwsim.c                        |  2 +-
 net/bridge/br_cfm.c                                  |  6 +++---
 net/bridge/br_mrp.c                                  |  8 ++++----
 net/ceph/messenger.c                                 |  3 ++-
 net/ceph/mon_client.c                                |  2 +-
 net/core/link_watch.c                                |  4 ++--
 net/core/skmsg.c                                     |  2 +-
 net/core/sock_diag.c                                 |  2 +-
 net/devlink/core.c                                   |  2 +-
 net/ipv4/inet_fragment.c                             |  2 +-
 net/netfilter/nf_conntrack_ecache.c                  |  2 +-
 net/openvswitch/dp_notify.c                          |  2 +-
 net/rds/ib_rdma.c                                    |  3 ++-
 net/rfkill/input.c                                   |  2 +-
 net/rxrpc/rxperf.c                                   |  2 +-
 net/smc/af_smc.c                                     |  6 +++---
 net/smc/smc_core.c                                   |  4 ++--
 net/tls/tls_device.c                                 |  2 +-
 net/unix/garbage.c                                   |  2 +-
 net/vmw_vsock/af_vsock.c                             |  2 +-
 net/vmw_vsock/virtio_transport.c                     |  2 +-
 net/vmw_vsock/vsock_loopback.c                       |  2 +-
 52 files changed, 88 insertions(+), 73 deletions(-)

-- 
2.51.0