linux-kernel - Re: [v3 PATCH 1/1] x86/resctrl: Add "*" shorthand to set io

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Message-ID: <77dabc50-a29a-4528-a724-bb51f0a94926@amd.com>
Date: Tue, 6 Jan 2026 10:49:02 -0600
From: Babu Moger <bmoger@....com>
To: Aaron Tomlin <atomlin@...mlin.com>, tony.luck@...el.com,
 reinette.chatre@...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: [v3 PATCH 1/1] x86/resctrl: Add "*" shorthand to set io_alloc CBM
 for all domains

Hi Aaron,

On 12/30/25 20:35, Aaron Tomlin wrote:
> Introduce a wildcard domain ID selector "*" for the io_alloc_cbm
> interface. This allows a user to update the Capacity Bitmask (CBM)
> across all cache domains in a single operation.
>
> Currently, configuring io_alloc_cbm requires an explicit ID for each
> domain, which is cumbersome on systems with high core counts and
> numerous cache clusters. Supporting a wildcard selector simplifies
> automation and management tasks.
>
> For example, a user can now write "*=0" to the io_alloc_cbm file to
> program every domain to the hardware-defined minimum CBM. Note that the
> value provided must still adhere to the constraints defined in the
> resource's min_cbm_bits.
>
> Signed-off-by: Aaron Tomlin <atomlin@...mlin.com>
> ---
>   Documentation/filesystems/resctrl.rst |  8 ++++
>   fs/resctrl/ctrlmondata.c              | 60 ++++++++++++++-------------
>   2 files changed, 40 insertions(+), 28 deletions(-)
>
> diff --git a/Documentation/filesystems/resctrl.rst b/Documentation/filesystems/resctrl.rst
> index 8c8ce678148a..e4d92c865e44 100644
> --- a/Documentation/filesystems/resctrl.rst
> +++ b/Documentation/filesystems/resctrl.rst
> @@ -215,6 +215,14 @@ related to allocation:
>   			# cat /sys/fs/resctrl/info/L3/io_alloc_cbm
>   			0=00ff;1=000f
>   
> +		Set each CBM to a specified value.
> +
> +		A special value "*" is required to represent all cache IDs.
> +
> +		Example::
> +
> +			# echo "*=0" > /sys/fs/resctrl/info/L3/io_alloc_cbm

To be consistent add the output also.

  # cat /sys/fs/resctrl/info/L3/io_alloc_cbm
      0=0;1=0

> +
>   		When CDP is enabled "io_alloc_cbm" associated with the CDP_DATA and CDP_CODE
>   		resources may reflect the same values. For example, values read from and
>   		written to /sys/fs/resctrl/info/L3DATA/io_alloc_cbm may be reflected by
> diff --git a/fs/resctrl/ctrlmondata.c b/fs/resctrl/ctrlmondata.c
> index b2d178d3556e..7b3119f91b9d 100644
> --- a/fs/resctrl/ctrlmondata.c
> +++ b/fs/resctrl/ctrlmondata.c
> @@ -873,41 +873,45 @@ static int resctrl_io_alloc_parse_line(char *line,  struct rdt_resource *r,
>   	struct rdt_ctrl_domain *d;
>   	char *dom = NULL, *id;
>   	unsigned long dom_id;
> +	bool update_all;
>   
> -next:
> -	if (!line || line[0] == '\0')
> -		return 0;
> +	while (line && line[0] != '\0') {
> +		update_all = false;
> +		dom = strsep(&line, ";");
> +		id = strsep(&dom, "=");
>   
> -	dom = strsep(&line, ";");
> -	id = strsep(&dom, "=");
> -	if (!dom || kstrtoul(id, 10, &dom_id)) {
> -		rdt_last_cmd_puts("Missing '=' or non-numeric domain\n");
> -		return -EINVAL;
> -	}
> +		if (id && !strcmp(id, "*")) {
> +			update_all = true;
> +		} else if (!dom || kstrtoul(id, 10, &dom_id)) {
> +			rdt_last_cmd_puts("Missing '=' or non-numeric domain\n");
> +			return -EINVAL;
> +		}
>   
> -	dom = strim(dom);
> -	list_for_each_entry(d, &r->ctrl_domains, hdr.list) {
> -		if (d->hdr.id == dom_id) {
> -			data.buf = dom;
> -			data.mode = RDT_MODE_SHAREABLE;
> -			data.closid = closid;
> -			if (parse_cbm(&data, s, d))
> -				return -EINVAL;
> -			/*
> -			 * Keep io_alloc CLOSID's CBM of CDP_CODE and CDP_DATA
> -			 * in sync.
> -			 */
> -			if (resctrl_arch_get_cdp_enabled(r->rid)) {
> -				peer_type = resctrl_peer_type(s->conf_type);
> -				memcpy(&d->staged_config[peer_type],
> -				       &d->staged_config[s->conf_type],
> -				       sizeof(d->staged_config[0]));
> +		dom = strim(dom);
> +		list_for_each_entry(d, &r->ctrl_domains, hdr.list) {
> +			if (update_all || d->hdr.id == dom_id) {
> +				data.buf = dom;
> +				data.mode = RDT_MODE_SHAREABLE;
> +				data.closid = closid;
> +				if (parse_cbm(&data, s, d))
> +					return -EINVAL;
> +				/*
> +				 * Keep io_alloc CLOSID's CBM of CDP_CODE and CDP_DATA
> +				 * in sync.
> +				 */
> +				if (resctrl_arch_get_cdp_enabled(r->rid)) {
> +					peer_type = resctrl_peer_type(s->conf_type);
> +					d->staged_config[peer_type] =
> +						d->staged_config[s->conf_type];
> +				}
> +
> +				if (!update_all)
> +					break;
>   			}
> -			goto next;
>   		}
>   	}
>   
> -	return -EINVAL;
> +	return 0;
>   }

Tested the patch and looks good to me.

Thanks

Babu




>   
>   ssize_t resctrl_io_alloc_cbm_write(struct kernfs_open_file *of, char *buf,