[RFC PATCH 8/8] PCI: Probe inline from node-local workqueue workers

[Pavol Sakac <sakacpav@amazon.de>]

pci_call_probe() dispatches each probe with queue_work_on() to a
housekeeping CPU of the device's node, except where it already probes
inline. A VF added by one of the preceding node-placed async VF-add
workers already executes on its device's node, so the dispatch buys it no
locality: it funnels every VF probe through the single CPU
cpumask_any_and() elects and re-serializes the parallel enable at the
probe step.

Call local_pci_probe() directly when the caller is a workqueue worker
(PF_WQ_WORKER) whose current CPU is on the device's node and in the same
HK_TYPE_DOMAIN housekeeping mask the dispatch elects from. The gate is
not VF-specific: any probe already running in a node-local housekeeping
kworker takes it, while a probe from a task that is not a worker keeps
the dispatch.

Assisted-by: LLM
Signed-off-by: Pavol Sakac <sakacpav@amazon.de>
---
 drivers/pci/pci-driver.c | 18 +++++++++++++++++-
 1 file changed, 17 insertions(+), 1 deletion(-)

diff --git a/drivers/pci/pci-driver.c b/drivers/pci/pci-driver.c
index e16aa59dd7ac..f5e12a5044cf 100644
--- a/drivers/pci/pci-driver.c
+++ b/drivers/pci/pci-driver.c
@@ -392,6 +392,22 @@ static bool pci_physfn_is_probed(struct pci_dev *dev)
 #endif
 }
 
+static bool pci_probe_inline(int node)
+{
+	/* The CPU is a placement hint; an unstable raw read is fine. */
+	int cpu = raw_smp_processor_id();
+	bool ret;
+
+	if (!(current->flags & PF_WQ_WORKER) || cpu_to_node(cpu) != node)
+		return false;
+
+	rcu_read_lock();
+	ret = housekeeping_cpu(cpu, HK_TYPE_DOMAIN);
+	rcu_read_unlock();
+
+	return ret;
+}
+
 static int pci_call_probe(struct pci_driver *drv, struct pci_dev *dev,
 			  const struct pci_device_id *id)
 {
@@ -412,7 +428,7 @@ static int pci_call_probe(struct pci_driver *drv, struct pci_dev *dev,
 	 * device is probed from work_on_cpu() of the Physical device.
 	 */
 	if (node < 0 || node >= MAX_NUMNODES || !node_online(node) ||
-	    pci_physfn_is_probed(dev)) {
+	    pci_physfn_is_probed(dev) || pci_probe_inline(node)) {
 		error = local_pci_probe(&ddi);
 	} else {
 		struct pci_probe_arg arg = { .ddi = &ddi };
-- 
2.47.3