linux-kernel - Re: [PATCH v2 1/3] fs/resctrl: Add helpers to check io

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Message-ID: <dcb81c71-6ced-4327-b32a-a431e31c4d93@intel.com>
Date: Tue, 16 Dec 2025 21:01:32 -0800
From: Reinette Chatre <reinette.chatre@...el.com>
To: Aaron Tomlin <atomlin@...mlin.com>, <tony.luck@...el.com>,
	<Dave.Martin@....com>, <james.morse@....com>, <babu.moger@....com>,
	<tglx@...utronix.de>, <mingo@...hat.com>, <bp@...en8.de>,
	<dave.hansen@...ux.intel.com>
CC: <sean@...e.io>, <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2 1/3] fs/resctrl: Add helpers to check io_alloc support
 and enabled state

Hi Aaron,

On 12/15/25 3:02 PM, Aaron Tomlin wrote:
> This patch introduces two helpers to validate io_alloc support and
> whether it is enabled. This reduces code duplication, clarifies
> intent, and preserves existing semantics and messages.
> 
> Signed-off-by: Aaron Tomlin <atomlin@...mlin.com>
> ---
>  fs/resctrl/ctrlmondata.c | 74 +++++++++++++++++++++++++++++-----------
>  1 file changed, 54 insertions(+), 20 deletions(-)
> 
> diff --git a/fs/resctrl/ctrlmondata.c b/fs/resctrl/ctrlmondata.c
> index b2d178d3556e..d2f9a4f2d887 100644
> --- a/fs/resctrl/ctrlmondata.c
> +++ b/fs/resctrl/ctrlmondata.c
> @@ -758,6 +758,50 @@ u32 resctrl_io_alloc_closid(struct rdt_resource *r)
>  		return resctrl_arch_get_num_closid(r) - 1;
>  }
>  
> +/*
> + * resctrl_io_alloc_supported() - Establish if io_alloc is supported
> + *
> + * @s: resctrl resource schema.
> + *
> + * This function must be called under the cpu hotplug lock
> + * and rdtgroup mutex
> + *
> + * Return: 0 on success, negative error code otherwise.
> + */
> +static inline int resctrl_io_alloc_supported(struct resctrl_schema *s)
> +{
> +	struct rdt_resource *r = s->res;
> +
> +	if (!r->cache.io_alloc.io_alloc_capable) {
> +		rdt_last_cmd_printf("io_alloc is not supported on %s\n", s->name);
> +		return -ENODEV;
> +	}
> +
> +	return 0;
> +}
> +
> +/*
> + * resctrl_io_alloc_enabled() - Establish if io_alloc is enabled
> + *
> + * @s: resctrl resource schema
> + *
> + * This function must be called under the cpu hotplug lock
> + * and rdtgroup mutex
> + *
> + * Return: 0 on success, negative error code otherwise.
> + */
> +static inline int resctrl_io_alloc_enabled(struct resctrl_schema *s)
> +{
> +	struct rdt_resource *r = s->res;
> +
> +	if (!resctrl_arch_get_io_alloc_enabled(r)) {
> +		rdt_last_cmd_printf("io_alloc is not enabled on %s\n", s->name);
> +		return -EINVAL;
> +	}
> +
> +	return 0;
> +}
> +
>  ssize_t resctrl_io_alloc_write(struct kernfs_open_file *of, char *buf,
>  			       size_t nbytes, loff_t off)
>  {
> @@ -777,11 +821,9 @@ ssize_t resctrl_io_alloc_write(struct kernfs_open_file *of, char *buf,
>  
>  	rdt_last_cmd_clear();
>  
> -	if (!r->cache.io_alloc_capable) {
> -		rdt_last_cmd_printf("io_alloc is not supported on %s\n", s->name);
> -		ret = -ENODEV;
> +	ret = resctrl_io_alloc_supported(s);
> +	if (ret)
>  		goto out_unlock;
> -	}
>  
>  	/* If the feature is already up to date, no action is needed. */
>  	if (resctrl_arch_get_io_alloc_enabled(r) == enable)
> @@ -839,17 +881,13 @@ int resctrl_io_alloc_cbm_show(struct kernfs_open_file *of, struct seq_file *seq,
>  
>  	rdt_last_cmd_clear();
>  
> -	if (!r->cache.io_alloc_capable) {
> -		rdt_last_cmd_printf("io_alloc is not supported on %s\n", s->name);
> -		ret = -ENODEV;
> +	ret = resctrl_io_alloc_supported(s);
> +	if (ret)
>  		goto out_unlock;
> -	}
>  
> -	if (!resctrl_arch_get_io_alloc_enabled(r)) {
> -		rdt_last_cmd_printf("io_alloc is not enabled on %s\n", s->name);
> -		ret = -EINVAL;
> +	ret = resctrl_io_alloc_enabled(s);
> +	if (ret)
>  		goto out_unlock;
> -	}
>  
>  	/*
>  	 * When CDP is enabled, the CBMs of the highest CLOSID of CDP_CODE and
> @@ -928,17 +966,13 @@ ssize_t resctrl_io_alloc_cbm_write(struct kernfs_open_file *of, char *buf,
>  	mutex_lock(&rdtgroup_mutex);
>  	rdt_last_cmd_clear();
>  
> -	if (!r->cache.io_alloc_capable) {
> -		rdt_last_cmd_printf("io_alloc is not supported on %s\n", s->name);
> -		ret = -ENODEV;
> +	ret = resctrl_io_alloc_supported(s);
> +	if (ret)
>  		goto out_unlock;
> -	}
>  
> -	if (!resctrl_arch_get_io_alloc_enabled(r)) {
> -		rdt_last_cmd_printf("io_alloc is not enabled on %s\n", s->name);
> -		ret = -EINVAL;
> +	ret = resctrl_io_alloc_enabled(s);
> +	if (ret)
>  		goto out_unlock;
> -	}
>  
>  	io_alloc_closid = resctrl_io_alloc_closid(r);
>  

How does this patch benefit the goal of this submission, which is to set identical CBM on
all domains?

If this change benefited this submission I should find these new helpers used in later patches
but they are not. This seems to be an unrelated and unnecessary change mixed with this
submission. It does not fix a bug nor does it support this submission and thus just adds noise when
considering the new feature for inclusion. This patch can be dropped. 

Reinette