linux-kernel - [PATCH 1/2] bcache: replace use of system_wq with system_percpu

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Message-ID: <20251105145043.231927-2-marco.crivellari@suse.com>
Date: Wed,  5 Nov 2025 15:50:42 +0100
From: Marco Crivellari <marco.crivellari@...e.com>
To: linux-kernel@...r.kernel.org,
	linux-bcache@...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>,
	Coly Li <colyli@...as.com>,
	Kent Overstreet <kent.overstreet@...ux.dev>
Subject: [PATCH 1/2] bcache: replace use of system_wq with system_percpu_wq

Currently if a user enqueues 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 consistency cannot be addressed without refactoring the API.

This patch continues the effort to refactor worqueue APIs, which has begun
with the change introducing new workqueues and a new alloc_workqueue flag:

commit 128ea9f6ccfb ("workqueue: Add system_percpu_wq and system_dfl_wq")
commit 930c2ea566af ("workqueue: Add new WQ_PERCPU flag")

system_wq should be the per-cpu workqueue, yet in this name nothing makes
that clear, so replace system_wq with system_percpu_wq.

The old wq (system_wq) will be kept for a few release cycles.

Suggested-by: Tejun Heo <tj@...nel.org>
Signed-off-by: Marco Crivellari <marco.crivellari@...e.com>
---
 drivers/md/bcache/super.c | 20 ++++++++++----------
 1 file changed, 10 insertions(+), 10 deletions(-)

diff --git a/drivers/md/bcache/super.c b/drivers/md/bcache/super.c
index 6d250e366412..8ce50753ae28 100644
--- a/drivers/md/bcache/super.c
+++ b/drivers/md/bcache/super.c
@@ -1388,7 +1388,7 @@ static CLOSURE_CALLBACK(cached_dev_flush)
 	bch_cache_accounting_destroy(&dc->accounting);
 	kobject_del(&d->kobj);
 
-	continue_at(cl, cached_dev_free, system_wq);
+	continue_at(cl, cached_dev_free, system_percpu_wq);
 }
 
 static int cached_dev_init(struct cached_dev *dc, unsigned int block_size)
@@ -1400,7 +1400,7 @@ static int cached_dev_init(struct cached_dev *dc, unsigned int block_size)
 	__module_get(THIS_MODULE);
 	INIT_LIST_HEAD(&dc->list);
 	closure_init(&dc->disk.cl, NULL);
-	set_closure_fn(&dc->disk.cl, cached_dev_flush, system_wq);
+	set_closure_fn(&dc->disk.cl, cached_dev_flush, system_percpu_wq);
 	kobject_init(&dc->disk.kobj, &bch_cached_dev_ktype);
 	INIT_WORK(&dc->detach, cached_dev_detach_finish);
 	sema_init(&dc->sb_write_mutex, 1);
@@ -1513,7 +1513,7 @@ static CLOSURE_CALLBACK(flash_dev_flush)
 	bcache_device_unlink(d);
 	mutex_unlock(&bch_register_lock);
 	kobject_del(&d->kobj);
-	continue_at(cl, flash_dev_free, system_wq);
+	continue_at(cl, flash_dev_free, system_percpu_wq);
 }
 
 static int flash_dev_run(struct cache_set *c, struct uuid_entry *u)
@@ -1525,7 +1525,7 @@ static int flash_dev_run(struct cache_set *c, struct uuid_entry *u)
 		goto err_ret;
 
 	closure_init(&d->cl, NULL);
-	set_closure_fn(&d->cl, flash_dev_flush, system_wq);
+	set_closure_fn(&d->cl, flash_dev_flush, system_percpu_wq);
 
 	kobject_init(&d->kobj, &bch_flash_dev_ktype);
 
@@ -1833,7 +1833,7 @@ static CLOSURE_CALLBACK(__cache_set_unregister)
 
 	mutex_unlock(&bch_register_lock);
 
-	continue_at(cl, cache_set_flush, system_wq);
+	continue_at(cl, cache_set_flush, system_percpu_wq);
 }
 
 void bch_cache_set_stop(struct cache_set *c)
@@ -1863,10 +1863,10 @@ struct cache_set *bch_cache_set_alloc(struct cache_sb *sb)
 
 	__module_get(THIS_MODULE);
 	closure_init(&c->cl, NULL);
-	set_closure_fn(&c->cl, cache_set_free, system_wq);
+	set_closure_fn(&c->cl, cache_set_free, system_percpu_wq);
 
 	closure_init(&c->caching, &c->cl);
-	set_closure_fn(&c->caching, __cache_set_unregister, system_wq);
+	set_closure_fn(&c->caching, __cache_set_unregister, system_percpu_wq);
 
 	/* Maybe create continue_at_noreturn() and use it here? */
 	closure_set_stopped(&c->cl);
@@ -2531,7 +2531,7 @@ static void register_device_async(struct async_reg_args *args)
 		INIT_DELAYED_WORK(&args->reg_work, register_cache_worker);
 
 	/* 10 jiffies is enough for a delay */
-	queue_delayed_work(system_wq, &args->reg_work, 10);
+	queue_delayed_work(system_percpu_wq, &args->reg_work, 10);
 }
 
 static void *alloc_holder_object(struct cache_sb *sb)
@@ -2912,11 +2912,11 @@ static int __init bcache_init(void)
 	/*
 	 * Let's not make this `WQ_MEM_RECLAIM` for the following reasons:
 	 *
-	 * 1. It used `system_wq` before which also does no memory reclaim.
+	 * 1. It used `system_percpu_wq` before which also does no memory reclaim.
 	 * 2. With `WQ_MEM_RECLAIM` desktop stalls, increased boot times, and
 	 *    reduced throughput can be observed.
 	 *
-	 * We still want to user our own queue to not congest the `system_wq`.
+	 * We still want to user our own queue to not congest the `system_percpu_wq`.
 	 */
 	bch_flush_wq = alloc_workqueue("bch_flush", 0, 0);
 	if (!bch_flush_wq)
-- 
2.51.1