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io_uring: replace use of system_unbound_wq with system_dfl_wq 

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.

system_unbound_wq should be the default workqueue so as not to enforce
locality constraints for random work whenever it's not required.

Adding system_dfl_wq to encourage its use when unbound work should be used.

queue_work() / queue_delayed_work() / mod_delayed_work() will now use the
new unbound wq: whether the user still use the old wq a warn will be
printed along with a wq redirect to the new one.

The old system_unbound_wq will be kept for a few release cycles.

Suggested-by: Tejun Heo <tj@kernel.org>
Signed-off-by: Marco Crivellari <marco.crivellari@suse.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
pull/1354/merge
Marco Crivellari 2025-09-05 11:02:40 +02:00 committed by Jens Axboe
parent 8577441d4a
commit 9f5f69d98e
1 changed files with 1 additions and 1 deletions
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io_uring/io_uring.c
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@ -3103,7 +3103,7 @@ static __cold void io_ring_ctx_wait_and_kill(struct io_ring_ctx *ctx)
INIT_WORK(&ctx->exit_work, io_ring_exit_work);
/*
* Use system_unbound_wq to avoid spawning tons of event kworkers
* Use system_dfl_wq to avoid spawning tons of event kworkers
* if we're exiting a ton of rings at the same time. It just adds
* noise and overhead, there's no discernable change in runtime
* over using system_percpu_wq.