[PATCH AUTOSEL 6.4 18/25] workqueue: Call wq_update_unbound_numa() on all CPUs in NUMA node on CPU hotplug

Sasha Levin
2023-09-09T00:39:19Z

From: Tejun Heo <tj@kernel.org>

[ Upstream commit 4cbfd3de737b9d00544ff0f673cb75fc37bffb6a ]

When a CPU went online or offline, wq_update_unbound_numa() was called only
on the CPU which was going up or down. This works fine because all CPUs on
the same NUMA node share the same pool_workqueue slot - one CPU updating it
updates it for everyone in the node.

However, future changes will make each CPU use a separate pool_workqueue
even when they're sharing the same worker_pool, which requires updating
pool_workqueue's for all CPUs which may be sharing the same pool_workqueue
on hotplug.

To accommodate the planned changes, this patch updates
workqueue_on/offline_cpu() so that they call wq_update_unbound_numa() for
all CPUs sharing the same NUMA node as the CPU going up or down. In the
current code, the second+ calls would be noops and there shouldn't be any
behavior changes.

* As wq_update_unbound_numa() is now called on multiple CPUs per each
hotplug event, @cpu is renamed to @hotplug_cpu and another @cpu argument
is added. The former indicates the CPU being hot[un]plugged and the latter
the CPU whose pool_workqueue is being updated.

* In wq_update_unbound_numa(), cpu_off is renamed to off_cpu for consistency
with the new @hotplug_cpu.

Signed-off-by: Tejun Heo <tj@kernel.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
kernel/workqueue.c | 34 +++++++++++++++++++++++++---------
1 file changed, 25 insertions(+), 9 deletions(-)

diff --git a/kernel/workqueue.c b/kernel/workqueue.c
index c913e333cce8e..21a6b15452935 100644
--- a/kernel/workqueue.c
+++ b/kernel/workqueue.c
@@ -4251,7 +4251,8 @@ int apply_workqueue_attrs(struct workqueue_struct *wq,
/**
* wq_update_unbound_numa - update NUMA affinity of a wq for CPU hot[un]plug
* @wq: the target workqueue
- * @cpu: the CPU coming up or going down
+ * @cpu: the CPU to update pool association for
+ * @hotplug_cpu: the CPU coming up or going down
* @online: whether @cpu is coming up or going down
*
* This function is to be called from %CPU_DOWN_PREPARE, %CPU_ONLINE and
@@ -4271,10 +4272,10 @@ int apply_workqueue_attrs(struct workqueue_struct *wq,
* CPU_DOWN_PREPARE.
*/
static void wq_update_unbound_numa(struct workqueue_struct *wq, int cpu,
- bool online)
+ int hotplug_cpu, bool online)
{
int node = cpu_to_node(cpu);
- int cpu_off = online ? -1 : cpu;
+ int off_cpu = online ? -1 : hotplug_cpu;
struct pool_workqueue *old_pwq = NULL, *pwq;
struct workqueue_attrs *target_attrs;
cpumask_t *cpumask;
@@ -4302,7 +4303,7 @@ static void wq_update_unbound_numa(struct workqueue_struct *wq, int cpu,
* and create a new one if they don't match. If the target cpumask
* equals the default pwq's, the default pwq should be used.
*/
- if (wq_calc_node_cpumask(wq->dfl_pwq->pool->attrs, node, cpu_off, cpumask)) {
+ if (wq_calc_node_cpumask(wq->dfl_pwq->pool->attrs, node, off_cpu, cpumask)) {
if (cpumask_equal(cpumask, pwq->pool->attrs->cpumask))
return;
} else {
@@ -5333,8 +5334,15 @@ int workqueue_online_cpu(unsigned int cpu)
}

/* update NUMA affinity of unbound workqueues */
- list_for_each_entry(wq, &workqueues, list)
- wq_update_unbound_numa(wq, cpu, true);
+ list_for_each_entry(wq, &workqueues, list) {
+ int tcpu;
+
+ for_each_possible_cpu(tcpu) {
+ if (cpu_to_node(tcpu) == cpu_to_node(cpu)) {
+ wq_update_unbound_numa(wq, tcpu, cpu, true);
+ }
+ }
+ }

mutex_unlock(&wq_pool_mutex);
return 0;
@@ -5352,8 +5360,15 @@ int workqueue_offline_cpu(unsigned int cpu)

/* update NUMA affinity of unbound workqueues */
mutex_lock(&wq_pool_mutex);
- list_for_each_entry(wq, &workqueues, list)
- wq_update_unbound_numa(wq, cpu, false);
+ list_for_each_entry(wq, &workqueues, list) {
+ int tcpu;
+
+ for_each_possible_cpu(tcpu) {
+ if (cpu_to_node(tcpu) == cpu_to_node(cpu)) {
+ wq_update_unbound_numa(wq, tcpu, cpu, false);
+ }
+ }
+ }
mutex_unlock(&wq_pool_mutex);

return 0;
@@ -6354,7 +6369,8 @@ void __init workqueue_init(void)
}

list_for_each_entry(wq, &workqueues, list) {
- wq_update_unbound_numa(wq, smp_processor_id(), true);
+ wq_update_unbound_numa(wq, smp_processor_id(), smp_processor_id(),
+ true);
WARN(init_rescuer(wq),
"workqueue: failed to create early rescuer for %s",
wq->name);
--
2.40.1