Re: [PATCH] PCI: Avoid unnecessary cpu_hotplug_disable() for non-NUMA devices

[Lukas Wunner <lukas@wunner.de>]

On Fri, May 22, 2026 at 02:11:24PM +0800, weipengliang wrote:
> When a PCI device is on an invalid/offline NUMA node or is a VF being
> probed from PF context, the code path calls local_pci_probe() directly
> without needing work_on_cpu(). In these cases, the cpu_hotplug_disable()
> / cpu_hotplug_enable() round-trip is unnecessary overhead.
> 
> Move cpu_hotplug_disable() into the NUMA-valid else branch so non-NUMA
> devices skip it entirely, returning early after local_pci_probe().

Hm, this will retain the cpu_hotplug_enable() outside the else-branch,
which isn't very readable IMHO.  How about moving cpu_hotplug_enable()
directly below each rcu_read_unlock() call?

> @@ -392,9 +391,13 @@ static int pci_call_probe(struct pci_driver *drv, struct pci_dev *dev,
>  	if (node < 0 || node >= MAX_NUMNODES || !node_online(node) ||
>  	    pci_physfn_is_probed(dev)) {
>  		error = local_pci_probe(&ddi);
> +		dev->is_probed = 0;
> +		return error;
>  	} else {
>  		struct pci_probe_arg arg = { .ddi = &ddi };
>  
> +		cpu_hotplug_disable();
> +
>  		INIT_WORK_ONSTACK(&arg.work, local_pci_probe_callback);
>  		/*
>  		 * The target election and the enqueue of the work must be within

I'd also move the cpu_hotplug_disable() below INIT_WORK_ONSTACK().
For one it minimizes the critical section, and also INIT_WORK_ONSTACK()
initializes a portion of "arg" declared immediately above, so it's
more readable to keep declaration + initialization together.

Thanks,

Lukas