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@xxxxxxxxxx>
Signed-off-by: Marco Crivellari <marco.crivellari@xxxxxxxx>
---
kernel/padata.c | 5 +++--
1 file changed, 3 insertions(+), 2 deletions(-)
diff --git a/kernel/padata.c b/kernel/padata.c
index 76b39fc8b326..26cc9b748b3d 100644
--- a/kernel/padata.c
+++ b/kernel/padata.c
@@ -1030,8 +1030,9 @@ struct padata_instance *padata_alloc(const char *name)
cpus_read_lock();
- pinst->serial_wq = alloc_workqueue("%s_serial", WQ_MEM_RECLAIM |
- WQ_CPU_INTENSIVE, 1, name);
+ pinst->serial_wq = alloc_workqueue("%s_serial",
+ WQ_MEM_RECLAIM | WQ_CPU_INTENSIVE | WQ_PERCPU,
+ 1, name);
if (!pinst->serial_wq)
goto err_put_cpus;
--
2.51.0
