linux-kernel - Re: [PATCH RFC 11/22] drivers: base: remove unnecessary call to register_cpu_under

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Message-ID: <955f2b95-76e4-4e68-830b-e6dd9f122dc1@redhat.com>
Date:   Mon, 13 Nov 2023 14:04:32 +1000
From:   Gavin Shan <gshan@...hat.com>
To:     "Russell King (Oracle)" <rmk+kernel@...linux.org.uk>,
        linux-pm@...r.kernel.org, loongarch@...ts.linux.dev,
        linux-acpi@...r.kernel.org, linux-arch@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        linux-riscv@...ts.infradead.org, kvmarm@...ts.linux.dev,
        x86@...nel.org, linux-csky@...r.kernel.org,
        linux-doc@...r.kernel.org, linux-ia64@...r.kernel.org,
        linux-parisc@...r.kernel.org
Cc:     Salil Mehta <salil.mehta@...wei.com>,
        Jean-Philippe Brucker <jean-philippe@...aro.org>,
        jianyong.wu@....com, justin.he@....com,
        James Morse <james.morse@....com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        "Rafael J. Wysocki" <rafael@...nel.org>
Subject: Re: [PATCH RFC 11/22] drivers: base: remove unnecessary call to
 register_cpu_under_node()

On 11/7/23 20:30, Russell King (Oracle) wrote:
> Since "drivers: base: Move cpu_dev_init() after node_dev_init()", we
> can remove some redundant code.
> 
> node_dev_init() will walk through the nodes calling register_one_node()
> on each. This will trickle down to __register_one_node() which walks
> all present CPUs, calling register_cpu_under_node() on each.
> 
> register_cpu_under_node() will call get_cpu_device(cpu) for each, which
> will return NULL until the CPU is registered using register_cpu(). This
> now happens _after_ node_dev_init().
> 
> Therefore, calling register_cpu_under_node() from __register_one_node()
> becomes a no-op, and can be removed.
> 
> Signed-off-by: Russell King (Oracle) <rmk+kernel@...linux.org.uk>
> ---
>   drivers/base/node.c | 7 -------
>   1 file changed, 7 deletions(-)
> 

__register_one_node() can be called in memory hot add path either. In that path,
a new NUMA node can be presented and becomes online. Does this become a problem
after the logic of associating CPU with newly added NUMA node?

Thanks,
Gavin

> diff --git a/drivers/base/node.c b/drivers/base/node.c
> index 493d533f8375..4d5ac7cf8757 100644
> --- a/drivers/base/node.c
> +++ b/drivers/base/node.c
> @@ -867,7 +867,6 @@ void register_memory_blocks_under_node(int nid, unsigned long start_pfn,
>   int __register_one_node(int nid)
>   {
>   	int error;
> -	int cpu;
>   
>   	node_devices[nid] = kzalloc(sizeof(struct node), GFP_KERNEL);
>   	if (!node_devices[nid])
> @@ -875,12 +874,6 @@ int __register_one_node(int nid)
>   
>   	error = register_node(node_devices[nid], nid);
>   
> -	/* link cpu under this node */
> -	for_each_present_cpu(cpu) {
> -		if (cpu_to_node(cpu) == nid)
> -			register_cpu_under_node(cpu, nid);
> -	}
> -
>   	INIT_LIST_HEAD(&node_devices[nid]->access_list);
>   	node_init_caches(nid);
>