linux-kernel - [PATCH 2/5] RDMA/core: WQ_PERCPU added to alloc

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Message-ID: <20251101163121.78400-3-marco.crivellari@suse.com>
Date: Sat,  1 Nov 2025 17:31:12 +0100
From: Marco Crivellari <marco.crivellari@...e.com>
To: linux-kernel@...r.kernel.org,
	linux-rdma@...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>,
	Jason Gunthorpe <jgg@...pe.ca>,
	Leon Romanovsky <leon@...nel.org>
Subject: [PATCH 2/5] RDMA/core: WQ_PERCPU added to alloc_workqueue users

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.

alloc_workqueue() treats all queues as per-CPU by default, while unbound
workqueues must opt-in via WQ_UNBOUND.

This default is suboptimal: most workloads benefit from unbound queues,
allowing the scheduler to place worker threads where they’re needed and
reducing noise when CPUs are isolated.

This change adds a new WQ_PERCPU flag to explicitly request
alloc_workqueue() to be per-cpu when WQ_UNBOUND has not been specified.

With the introduction of the WQ_PERCPU flag (equivalent to !WQ_UNBOUND),
any alloc_workqueue() caller that doesn’t explicitly specify WQ_UNBOUND
must now use WQ_PERCPU.

Once migration is complete, WQ_UNBOUND can be removed and unbound will
become the implicit default.

Suggested-by: Tejun Heo <tj@...nel.org>
Signed-off-by: Marco Crivellari <marco.crivellari@...e.com>
---
 drivers/infiniband/core/cm.c     | 2 +-
 drivers/infiniband/core/device.c | 4 ++--
 2 files changed, 3 insertions(+), 3 deletions(-)

diff --git a/drivers/infiniband/core/cm.c b/drivers/infiniband/core/cm.c
index 01bede8ba105..47d0022cadac 100644
--- a/drivers/infiniband/core/cm.c
+++ b/drivers/infiniband/core/cm.c
@@ -4518,7 +4518,7 @@ static int __init ib_cm_init(void)
 	get_random_bytes(&cm.random_id_operand, sizeof cm.random_id_operand);
 	INIT_LIST_HEAD(&cm.timewait_list);

-	cm.wq = alloc_workqueue("ib_cm", 0, 1);
+	cm.wq = alloc_workqueue("ib_cm", WQ_PERCPU, 1);
 	if (!cm.wq) {
 		ret = -ENOMEM;
 		goto error2;
diff --git a/drivers/infiniband/core/device.c b/drivers/infiniband/core/device.c
index b4f3c835844a..13e8a1714bbd 100644
--- a/drivers/infiniband/core/device.c
+++ b/drivers/infiniband/core/device.c
@@ -3021,7 +3021,7 @@ static int __init ib_core_init(void)
 {
 	int ret = -ENOMEM;

-	ib_wq = alloc_workqueue("infiniband", 0, 0);
+	ib_wq = alloc_workqueue("infiniband", WQ_PERCPU, 0);
 	if (!ib_wq)
 		return -ENOMEM;

@@ -3031,7 +3031,7 @@ static int __init ib_core_init(void)
 		goto err;

 	ib_comp_wq = alloc_workqueue("ib-comp-wq",
-			WQ_HIGHPRI | WQ_MEM_RECLAIM | WQ_SYSFS, 0);
+			WQ_HIGHPRI | WQ_MEM_RECLAIM | WQ_SYSFS | WQ_PERCPU, 0);
 	if (!ib_comp_wq)
 		goto err_unbound;

-- 
2.51.0