Subject: Re: [PATCH 04/13] powerpc/xive: Use cpu_to_node() instead of ibm, chip-id property

From: "Aneesh Kumar K.V" <[email-masked]>
Date: Wed, 09 Dec 2020 10:09:18 +0530

Cédric Le Goater <[email-masked]> writes:

> The 'chip_id' field of the XIVE CPU structure is used to choose a
> target for a source located on the same chip when possible. This field
> is assigned on the PowerNV platform using the "ibm,chip-id" property
> on pSeries under KVM when NUMA nodes are defined but it is undefined
> under PowerVM. The XIVE source structure has a similar field
> 'src_chip' which is only assigned on the PowerNV platform.
>
> cpu_to_node() returns a compatible value on all platforms, 0 being the
> default node. It will also give us the opportunity to set the affinity
> of a source on pSeries when we can localize them.

But we should avoid assuming that linux numa node number is equivalent
to chip id [1]. What do we expect this value represents on virtualized
platforms like PowerVM and KVM? Is this used for a hcall?

[1] https://lore.kernel.org/linuxppc-dev/[email-masked]

>
> Signed-off-by: Cédric Le Goater <[email-masked]>
> ---
>  arch/powerpc/sysdev/xive/common.c | 7 +------
>  1 file changed, 1 insertion(+), 6 deletions(-)
>
> diff --git a/arch/powerpc/sysdev/xive/common.c b/arch/powerpc/sysdev/xive/common.c
> index ee375daf8114..605238ca65e4 100644
> --- a/arch/powerpc/sysdev/xive/common.c
> +++ b/arch/powerpc/sysdev/xive/common.c
> @@ -1342,16 +1342,11 @@ static int xive_prepare_cpu(unsigned int cpu)
>  
>  	xc = per_cpu(xive_cpu, cpu);
>  	if (!xc) {
> -		struct device_node *np;
> -
>  		xc = kzalloc_node(sizeof(struct xive_cpu),
>  				  GFP_KERNEL, cpu_to_node(cpu));
>  		if (!xc)
>  			return -ENOMEM;
> -		np = of_get_cpu_node(cpu, NULL);
> -		if (np)
> -			xc->chip_id = of_get_ibm_chip_id(np);
> -		of_node_put(np);
> +		xc->chip_id = cpu_to_node(cpu);
>  		xc->hw_ipi = XIVE_BAD_IRQ;
>  
>  		per_cpu(xive_cpu, cpu) = xc;
> -- 
> 2.26.2