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Message-ID: <20250905090505.104882-1-marco.crivellari@suse.com>
Date: Fri, 5 Sep 2025 11:05:02 +0200
From: Marco Crivellari <marco.crivellari@...e.com>
To: linux-kernel@...r.kernel.org,
netdev@...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>,
"David S . Miller" <davem@...emloft.net>,
Eric Dumazet <edumazet@...gle.com>,
Jakub Kicinski <kuba@...nel.org>,
Paolo Abeni <pabeni@...hat.com>
Subject: [PATCH net-next 0/3] net: 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):
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/wireless/ath/ath6kl/usb.c | 2 +-
drivers/net/wireless/intel/ipw2x00/ipw2100.c | 6 +++---
drivers/net/wireless/intel/ipw2x00/ipw2200.c | 2 +-
drivers/net/wireless/intel/iwlwifi/fw/dbg.c | 4 ++--
drivers/net/wireless/intel/iwlwifi/iwl-trans.h | 2 +-
drivers/net/wireless/intel/iwlwifi/mvm/tdls.c | 6 +++---
drivers/net/wireless/marvell/libertas/if_sdio.c | 3 ++-
drivers/net/wireless/marvell/libertas/if_spi.c | 3 ++-
drivers/net/wireless/marvell/libertas_tf/main.c | 2 +-
drivers/net/wireless/mediatek/mt76/mt7921/init.c | 2 +-
drivers/net/wireless/mediatek/mt76/mt7925/init.c | 2 +-
drivers/net/wireless/quantenna/qtnfmac/core.c | 3 ++-
drivers/net/wireless/realtek/rtlwifi/base.c | 2 +-
drivers/net/wireless/realtek/rtw88/usb.c | 3 ++-
drivers/net/wireless/silabs/wfx/main.c | 2 +-
drivers/net/wireless/st/cw1200/bh.c | 4 ++--
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 +-
net/wireless/core.c | 4 ++--
net/wireless/sysfs.c | 2 +-
70 files changed, 117 insertions(+), 98 deletions(-)
--
2.51.0
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