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>
---
virt/kvm/eventfd.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/virt/kvm/eventfd.c b/virt/kvm/eventfd.c
index 11e5d1e3f12e..4f0bdd67edb2 100644
--- a/virt/kvm/eventfd.c
+++ b/virt/kvm/eventfd.c
@@ -662,7 +662,7 @@ bool kvm_notify_irqfd_resampler(struct kvm *kvm,
*/
int kvm_irqfd_init(void)
{
- irqfd_cleanup_wq = alloc_workqueue("kvm-irqfd-cleanup", 0, 0);
+ irqfd_cleanup_wq = alloc_workqueue("kvm-irqfd-cleanup", WQ_PERCPU, 0);
if (!irqfd_cleanup_wq)
return -ENOMEM;
--
2.51.0
