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bpf: WQ_PERCPU added to alloc_workqueue users

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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 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 patch adds a new WQ_PERCPU flag to explicitly request the use of
the per-CPU behavior. Both flags coexist for one release cycle to allow
callers to transition their calls.

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

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.

All existing users have been updated accordingly.

Suggested-by: Tejun Heo <tj@kernel.org>
Signed-off-by: Marco Crivellari <marco.crivellari@suse.com>
Link: https://lore.kernel.org/r/20250905085309.94596-4-marco.crivellari@suse.com
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
This commit is contained in:
Marco Crivellari 2025-09-05 10:53:09 +02:00 • committed by Alexei Starovoitov
parent 0409819a00
commit a857210b10
1 changed files with 2 additions and 1 deletions
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3
kernel/bpf/cgroup.c
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@ -34,7 +34,8 @@ static struct workqueue_struct *cgroup_bpf_destroy_wq;
static int __init cgroup_bpf_wq_init(void)
{
cgroup_bpf_destroy_wq = alloc_workqueue("cgroup_bpf_destroy", 0, 1);
cgroup_bpf_destroy_wq = alloc_workqueue("cgroup_bpf_destroy",
WQ_PERCPU, 1);
if (!cgroup_bpf_destroy_wq)
panic("Failed to alloc workqueue for cgroup bpf destroy.\n");
return 0;