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Wed, 05 Nov 2025 06:50:55 -0800 (PST) Received: from localhost.localdomain ([2a00:6d43:105:c401:e307:1a37:2e76:ce91]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-429dc1f5ccasm10662873f8f.25.2025.11.05.06.50.55 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 05 Nov 2025 06:50:55 -0800 (PST) From: Marco Crivellari To: linux-kernel@vger.kernel.org, linux-bcache@vger.kernel.org Cc: Tejun Heo , Lai Jiangshan , Frederic Weisbecker , Sebastian Andrzej Siewior , Marco Crivellari , Michal Hocko , Coly Li , Kent Overstreet Subject: [PATCH 2/2] bcache: WQ_PERCPU added to alloc_workqueue users Date: Wed, 5 Nov 2025 15:50:43 +0100 Message-ID: <20251105145043.231927-3-marco.crivellari@suse.com> X-Mailer: git-send-email 2.51.1 In-Reply-To: <20251105145043.231927-1-marco.crivellari@suse.com> References: <20251105145043.231927-1-marco.crivellari@suse.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: quoted-printable 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=E2=80=99re needed= and reducing noise when CPUs are isolated. 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") 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=E2=80=99t explicitly specify WQ_UNB= OUND 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 Signed-off-by: Marco Crivellari --- drivers/md/bcache/btree.c | 3 ++- drivers/md/bcache/super.c | 10 ++++++---- drivers/md/bcache/writeback.c | 2 +- 3 files changed, 9 insertions(+), 6 deletions(-) diff --git a/drivers/md/bcache/btree.c b/drivers/md/bcache/btree.c index 210b59007d98..e7b8c688d963 100644 --- a/drivers/md/bcache/btree.c +++ b/drivers/md/bcache/btree.c @@ -2822,7 +2822,8 @@ void bch_btree_exit(void) =20 int __init bch_btree_init(void) { - btree_io_wq =3D alloc_workqueue("bch_btree_io", WQ_MEM_RECLAIM, 0); + btree_io_wq =3D alloc_workqueue("bch_btree_io", + WQ_MEM_RECLAIM | WQ_PERCPU, 0); if (!btree_io_wq) return -ENOMEM; =20 diff --git a/drivers/md/bcache/super.c b/drivers/md/bcache/super.c index 8ce50753ae28..a0425351c179 100644 --- a/drivers/md/bcache/super.c +++ b/drivers/md/bcache/super.c @@ -1939,7 +1939,8 @@ struct cache_set *bch_cache_set_alloc(struct cache_sb= *sb) if (!c->uuids) goto err; =20 - c->moving_gc_wq =3D alloc_workqueue("bcache_gc", WQ_MEM_RECLAIM, 0); + c->moving_gc_wq =3D alloc_workqueue("bcache_gc", + WQ_MEM_RECLAIM | WQ_PERCPU, 0); if (!c->moving_gc_wq) goto err; =20 @@ -2905,7 +2906,7 @@ static int __init bcache_init(void) if (bch_btree_init()) goto err; =20 - bcache_wq =3D alloc_workqueue("bcache", WQ_MEM_RECLAIM, 0); + bcache_wq =3D alloc_workqueue("bcache", WQ_MEM_RECLAIM | WQ_PERCPU, 0); if (!bcache_wq) goto err; =20 @@ -2918,11 +2919,12 @@ static int __init bcache_init(void) * * We still want to user our own queue to not congest the `system_percpu_= wq`. */ - bch_flush_wq =3D alloc_workqueue("bch_flush", 0, 0); + bch_flush_wq =3D alloc_workqueue("bch_flush", WQ_PERCPU, 0); if (!bch_flush_wq) goto err; =20 - bch_journal_wq =3D alloc_workqueue("bch_journal", WQ_MEM_RECLAIM, 0); + bch_journal_wq =3D alloc_workqueue("bch_journal", + WQ_MEM_RECLAIM | WQ_PERCPU, 0); if (!bch_journal_wq) goto err; =20 diff --git a/drivers/md/bcache/writeback.c b/drivers/md/bcache/writeback.c index 6ba73dc1a3df..ccbd9a8f28f5 100644 --- a/drivers/md/bcache/writeback.c +++ b/drivers/md/bcache/writeback.c @@ -1076,7 +1076,7 @@ void bch_cached_dev_writeback_init(struct cached_dev = *dc) int bch_cached_dev_writeback_start(struct cached_dev *dc) { dc->writeback_write_wq =3D alloc_workqueue("bcache_writeback_wq", - WQ_MEM_RECLAIM, 0); + WQ_MEM_RECLAIM | WQ_PERCPU, 0); if (!dc->writeback_write_wq) return -ENOMEM; =20 --=20 2.51.1