linux-kernel - Re: [PATCH v8 16/21] x86/resctrl: Always initialise rid field in rdt_resources

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Message-ID: <Z_6uoqLNCXuc2COl@agluck-desk3>
Date: Tue, 15 Apr 2025 12:08:18 -0700
From: "Luck, Tony" <tony.luck@...el.com>
To: James Morse <james.morse@....com>
Cc: x86@...nel.org, linux-kernel@...r.kernel.org,
	Reinette Chatre <reinette.chatre@...el.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
	H Peter Anvin <hpa@...or.com>, Babu Moger <Babu.Moger@....com>,
	shameerali.kolothum.thodi@...wei.com,
	D Scott Phillips OS <scott@...amperecomputing.com>,
	carl@...amperecomputing.com, lcherian@...vell.com,
	bobo.shaobowang@...wei.com, tan.shaopeng@...itsu.com,
	baolin.wang@...ux.alibaba.com, Jamie Iles <quic_jiles@...cinc.com>,
	Xin Hao <xhao@...ux.alibaba.com>, peternewman@...gle.com,
	dfustini@...libre.com, amitsinght@...vell.com,
	David Hildenbrand <david@...hat.com>,
	Rex Nie <rex.nie@...uarmicro.com>,
	Dave Martin <dave.martin@....com>, Koba Ko <kobak@...dia.com>,
	Shanker Donthineni <sdonthineni@...dia.com>, fenghuay@...dia.com
Subject: Re: [PATCH v8 16/21] x86/resctrl: Always initialise rid field in
 rdt_resources_all[]

On Fri, Apr 11, 2025 at 04:42:24PM +0000, James Morse wrote:
> x86 has an array, rdt_resources_all[], of all possible resources.
> The for-each-resource walkers depend on the rid field of all
> resources being initialised.
> 
> If the array ever grows due to another architecture adding a resource
> type that is not defined on x86, the for-each-resources walkers will
> loop forever.

This feels a bit weird. Having rdt_resources_all[] be a "swiss cheese"
array full of holes where other architectures defined events that aren't
supported by x86.

But it does work, so it can go in like this. But someday I may revisit
some experimental patches I did a while back that:
1) Split the rdt_resource structure into separate "ctrl" and "mon"
pieces.
2) Replaced this array with a pair of lists, one each for enabled
ctrl and mon resources.
3) Changed the resource walkers to use list_for_each*() macros.

> 
> Initialise all the rid values in resctrl_arch_late_init() before
> any for-each-resource walker can be called.
> 
> Signed-off-by: James Morse <james.morse@....com>
> 
> ---
> Changes since v7:
>  * Split out of a previous patch due to a botched merged conflict.
> ---
>  arch/x86/kernel/cpu/resctrl/core.c | 10 +++++-----
>  1 file changed, 5 insertions(+), 5 deletions(-)
> 
> diff --git a/arch/x86/kernel/cpu/resctrl/core.c b/arch/x86/kernel/cpu/resctrl/core.c
> index 58d7c6accdf2..ce684da600bc 100644
> --- a/arch/x86/kernel/cpu/resctrl/core.c
> +++ b/arch/x86/kernel/cpu/resctrl/core.c
> @@ -60,7 +60,6 @@ struct rdt_hw_resource rdt_resources_all[RDT_NUM_RESOURCES] = {
>  	[RDT_RESOURCE_L3] =
>  	{
>  		.r_resctrl = {
> -			.rid			= RDT_RESOURCE_L3,
>  			.name			= "L3",
>  			.ctrl_scope		= RESCTRL_L3_CACHE,
>  			.mon_scope		= RESCTRL_L3_CACHE,
> @@ -74,7 +73,6 @@ struct rdt_hw_resource rdt_resources_all[RDT_NUM_RESOURCES] = {
>  	[RDT_RESOURCE_L2] =
>  	{
>  		.r_resctrl = {
> -			.rid			= RDT_RESOURCE_L2,
>  			.name			= "L2",
>  			.ctrl_scope		= RESCTRL_L2_CACHE,
>  			.ctrl_domains		= ctrl_domain_init(RDT_RESOURCE_L2),
> @@ -86,7 +84,6 @@ struct rdt_hw_resource rdt_resources_all[RDT_NUM_RESOURCES] = {
>  	[RDT_RESOURCE_MBA] =
>  	{
>  		.r_resctrl = {
> -			.rid			= RDT_RESOURCE_MBA,
>  			.name			= "MB",
>  			.ctrl_scope		= RESCTRL_L3_CACHE,
>  			.ctrl_domains		= ctrl_domain_init(RDT_RESOURCE_MBA),
> @@ -96,7 +93,6 @@ struct rdt_hw_resource rdt_resources_all[RDT_NUM_RESOURCES] = {
>  	[RDT_RESOURCE_SMBA] =
>  	{
>  		.r_resctrl = {
> -			.rid			= RDT_RESOURCE_SMBA,
>  			.name			= "SMBA",
>  			.ctrl_scope		= RESCTRL_L3_CACHE,
>  			.ctrl_domains		= ctrl_domain_init(RDT_RESOURCE_SMBA),
> @@ -996,7 +992,11 @@ void resctrl_cpu_detect(struct cpuinfo_x86 *c)
>  static int __init resctrl_arch_late_init(void)
>  {
>  	struct rdt_resource *r;
> -	int state, ret;
> +	int state, ret, i;
> +
> +	/* Initialise all rid values for_each_rdt_resource() */
> +	for (i = 0; i < RDT_NUM_RESOURCES; i++)
> +		rdt_resources_all[i].r_resctrl.rid = i;
>  
>  	/*
>  	 * Initialize functions(or definitions) that are different
> -- 
> 2.20.1

-Tony