linux-kernel - Re: [PATCH v2] cpu-topology: Skip the exist but not possible cpu nodes

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Date:   Mon, 13 Jan 2020 10:19:22 +0000
From:   Sudeep Holla <sudeep.holla@....com>
To:     Zeng Tao <prime.zeng@...ilicon.com>
Cc:     linuxarm@...wei.com,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        "Rafael J. Wysocki" <rafael@...nel.org>,
        Sudeep Holla <sudeep.holla@....com>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2] cpu-topology: Skip the exist but not possible cpu
 nodes

On Sat, Jan 11, 2020 at 02:53:40PM +0800, Zeng Tao wrote:
> When CONFIG_NR_CPUS is smaller than the cpu nodes defined in the device
> tree, all the cpu nodes parsing will fail.
> And this is not reasonable for a legal device tree configs.
> In this patch, skip such cpu nodes rather than return an error.
> With CONFIG_NR_CPUS = 128 and cpus nodes num in device tree is 130,
> The following warning messages will be print during boot:
> CPU node for /cpus/cpu@128 exist but the possible cpu range is :0-127
> CPU node for /cpus/cpu@129 exist but the possible cpu range is :0-127
> CPU node for /cpus/cpu@130 exist but the possible cpu range is :0-127
> 
> Signed-off-by: Zeng Tao <prime.zeng@...ilicon.com>
> ---
> Changelog:
> v1->v2:
>  -Remove redundant -ENODEV assignment in get_cpu_for_node
>  -Add comment to describe the get_cpu_for_node return values
>  -Add skip process for cpu threads
>  -Update the commit log with more detail
> ---
>  drivers/base/arch_topology.c | 37 +++++++++++++++++++++++++++++--------
>  1 file changed, 29 insertions(+), 8 deletions(-)
> 
> diff --git a/drivers/base/arch_topology.c b/drivers/base/arch_topology.c
> index 5fe44b3..01f0e21 100644
> --- a/drivers/base/arch_topology.c
> +++ b/drivers/base/arch_topology.c
> @@ -248,22 +248,44 @@ core_initcall(free_raw_capacity);
>  #endif
>  
>  #if defined(CONFIG_ARM64) || defined(CONFIG_RISCV)
> +/*
> + * This function returns the logic cpu number of the node.
> + * There are totally three kinds of return values:
> + * (1) logic cpu number which is > 0.
> + * (2) -ENDEV when the node is valid one which can be found in the device tree
> + * but there is no possible cpu nodes to match, when the CONFIG_NR_CPUS is
> + * smaller than cpus node numbers in device tree, this will happen. It's
> + * suggested to just ignore this case.

s/ENDEV/ENODEV/

Also as I mentioned earlier, I prefer not to add any extra logic here
other than the above comment to make it explicit. This triggers unnecessary
warnings when someone boots with limited CPUs for valid reasons.


> + * (3) -EINVAL when other errors occur.
> + */
>  static int __init get_cpu_for_node(struct device_node *node)
>  {
> -	struct device_node *cpu_node;
> +	struct device_node *cpu_node, *t;
>  	int cpu;
> +	bool found = false;
>  
>  	cpu_node = of_parse_phandle(node, "cpu", 0);
>  	if (!cpu_node)
> -		return -1;
> +		return -EINVAL;
> +
> +	for_each_of_cpu_node(t)
> +		if (t == cpu_node) {
> +			found = true;
> +			break;
> +		}
> +
> +	if (!found) {
> +		pr_crit("Unable to find CPU node for %pOF\n", cpu_node);
> +		return -EINVAL;
> +	}
>  
>  	cpu = of_cpu_node_to_id(cpu_node);
>  	if (cpu >= 0)
>  		topology_parse_cpu_capacity(cpu_node, cpu);
>  	else
> -		pr_crit("Unable to find CPU node for %pOF\n", cpu_node);
> +		pr_warn("CPU node for %pOF exist but the possible cpu range is :%*pbl\n",
> +			cpu_node, cpumask_pr_args(cpu_possible_mask));
>  
> -	of_node_put(cpu_node);

Why is this dropped ?

--
Regards,
Sudeep