Re: [PATCH v7 10/10] fs/resctrl: Introduce interface to modify io_alloc Capacity Bit Masks

[Reinette Chatre <reinette.chatre@intel.com>]

Hi Babu,

On 7/10/25 10:16 AM, Babu Moger wrote:
> "io_alloc" feature enables direct insertion of data from I/O devices into
> the cache. By directly caching data from I/O devices rather than first
> storing the I/O data in DRAM, it reduces the demands on DRAM bandwidth and
> reduces latency to the processor consuming the I/O data.
> 
> Provide the interface to modify io_alloc CBMs (Capacity Bit Mask) when

"Provide the interface to modify io_alloc CBMs (Capacity Bit Mask) when feature is
enabled." ->
"Enable users to modify io_alloc CBMs (Capacity Bit Masks) via the io_alloc_cbm
resctrl file when io_alloc is enabled."?

> feature is enabled. Update the CBMs for both CDP_DATA and CDP_CODE when CDP
> is enabled.
> 
> Signed-off-by: Babu Moger <babu.moger@amd.com>
> ---

...

> ---
>  Documentation/filesystems/resctrl.rst |   8 ++
>  fs/resctrl/ctrlmondata.c              |   4 +-
>  fs/resctrl/internal.h                 |   2 +
>  fs/resctrl/rdtgroup.c                 | 112 +++++++++++++++++++++++++-
>  4 files changed, 123 insertions(+), 3 deletions(-)
> 
> diff --git a/Documentation/filesystems/resctrl.rst b/Documentation/filesystems/resctrl.rst
> index c22a9dd667cd..b9c3ffdec27f 100644
> --- a/Documentation/filesystems/resctrl.rst
> +++ b/Documentation/filesystems/resctrl.rst
> @@ -189,6 +189,14 @@ related to allocation:
>  			# cat /sys/fs/resctrl/info/L3/io_alloc_cbm
>  			0=ffff;1=ffff
>  
> +		CBMs can be configured by writing to the interface.
> +
> +		Example::
> +
> +			# echo 1=FF > /sys/fs/resctrl/info/L3/io_alloc_cbm
> +			# cat /sys/fs/resctrl/info/L3/io_alloc_cbm
> +			0=ffff;1=00ff
> +
>  		When CDP is enabled "io_alloc_cbm" associated with the DATA and 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 5c16557fb7a8..23c72a5ac043 100644
> --- a/fs/resctrl/ctrlmondata.c
> +++ b/fs/resctrl/ctrlmondata.c
> @@ -148,8 +148,8 @@ static bool cbm_validate(char *buf, u32 *data, struct rdt_resource *r)
>   * Read one cache bit mask (hex). Check that it is valid for the current
>   * resource type.
>   */
> -static int parse_cbm(struct rdt_parse_data *data, struct resctrl_schema *s,
> -		     struct rdt_ctrl_domain *d)
> +int parse_cbm(struct rdt_parse_data *data, struct resctrl_schema *s,
> +	      struct rdt_ctrl_domain *d)

This can remain static by moving caller to ctrlmondata.c

>  {
>  	enum rdtgrp_mode mode = data->mode;
>  	struct resctrl_staged_config *cfg;
> diff --git a/fs/resctrl/internal.h b/fs/resctrl/internal.h
> index ab76a1e2e679..011564e69ed5 100644
> --- a/fs/resctrl/internal.h
> +++ b/fs/resctrl/internal.h
> @@ -382,6 +382,8 @@ bool closid_allocated(unsigned int closid);
>  int resctrl_find_cleanest_closid(void);
>  void show_doms(struct seq_file *s, struct resctrl_schema *schema,
>  	       char *name, int closid);
> +int parse_cbm(struct rdt_parse_data *data, struct resctrl_schema *s,
> +	      struct rdt_ctrl_domain *d);
>  
>  #ifdef CONFIG_RESCTRL_FS_PSEUDO_LOCK
>  int rdtgroup_locksetup_enter(struct rdtgroup *rdtgrp);
> diff --git a/fs/resctrl/rdtgroup.c b/fs/resctrl/rdtgroup.c
> index 008657e43656..1093ec5e385b 100644
> --- a/fs/resctrl/rdtgroup.c
> +++ b/fs/resctrl/rdtgroup.c
> @@ -2036,6 +2036,115 @@ static int resctrl_io_alloc_cbm_show(struct kernfs_open_file *of,
>  	return ret;
>  }
>  
> +static int resctrl_io_alloc_parse_line(char *line,  struct rdt_resource *r,
> +				       struct resctrl_schema *s, u32 closid)

Please move to ctrlmondata.c

> +{
> +	struct rdt_parse_data data;
> +	struct rdt_ctrl_domain *d;
> +	char *dom = NULL, *id;
> +	unsigned long dom_id;
> +
> +next:
> +	if (!line || line[0] == '\0')
> +		return 0;
> +
> +	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;
> +	}
> +
> +	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;
> +			goto next;
> +		}
> +	}
> +	return -EINVAL;
> +}
> +
> +static ssize_t resctrl_io_alloc_cbm_write(struct kernfs_open_file *of,
> +					  char *buf, size_t nbytes, loff_t off)

Please move to ctrlmondata.c

> +{
> +	struct resctrl_schema *s = rdt_kn_parent_priv(of->kn);
> +	enum resctrl_conf_type peer_type;
> +	struct rdt_resource *r = s->res;
> +	struct resctrl_schema *peer_s;
> +	u32 io_alloc_closid;
> +	char *peer_buf;
> +	int ret = 0;
> +
> +	/* Valid input requires a trailing newline */
> +	if (nbytes == 0 || buf[nbytes - 1] != '\n')
> +		return -EINVAL;
> +
> +	buf[nbytes - 1] = '\0';
> +
> +	cpus_read_lock();
> +	mutex_lock(&rdtgroup_mutex);
> +
> +	if (!r->cache.io_alloc_capable) {
> +		rdt_last_cmd_printf("io_alloc is not supported on %s\n", s->name);

rdt_last_cmd_clear() is required before any write to the buffer.

> +		ret = -EINVAL;
> +		goto out_unlock;
> +	}
> +
> +	rdt_last_cmd_clear();
> +	rdt_staged_configs_clear();
> +
> +	if (!resctrl_arch_get_io_alloc_enabled(r)) {
> +		rdt_last_cmd_printf("io_alloc is not enabled on %s\n", s->name);
> +		ret = -EINVAL;

Inconsistent error codes when io_alloc is not enabled.  resctrl_io_alloc_write()
and resctrl_io_alloc_cbm_show() returns -ENODEV.

> +		goto out_unlock;
> +	}
> +
> +	io_alloc_closid = resctrl_io_alloc_closid(r);
> +
> +	/*
> +	 * When CDP is enabled, update the schema for both CDP_DATA and CDP_CODE.
> +	 * Since the buffer is altered during parsing, create a copy to handle
> +	 * peer schemata separately.
> +	 */
> +	if (resctrl_arch_get_cdp_enabled(r->rid)) {
> +		peer_type = resctrl_peer_type(s->conf_type);
> +		peer_s = resctrl_get_schema(peer_type);
> +		peer_buf = kmalloc(nbytes, GFP_KERNEL);
> +		if (!peer_buf) {
> +			rdt_last_cmd_puts("Out of Memory - io_alloc update failed\n");
> +			ret = -ENOMEM;
> +			goto out_unlock;
> +		}
> +
> +		memcpy(peer_buf, buf, nbytes);
> +
> +		if (peer_s)
> +			ret = resctrl_io_alloc_parse_line(peer_buf, r, peer_s, io_alloc_closid);

Similar to resctrl_io_alloc_write() this looks unnecessary. I think this can be simplified
by moving the CDP check to resctrl_io_alloc_parse_line() where the provided CBM can be parsed
*once* and the staged config of a CDP type just copied to the staged config of its peer type.

> +
> +		kfree(peer_buf);
> +	}
> +
> +	if (!ret)
> +		ret = resctrl_io_alloc_parse_line(buf, r, s, io_alloc_closid);
> +
> +	if (ret)
> +		goto out_unlock;
> +
> +	ret = resctrl_arch_update_domains(r, io_alloc_closid);
> +
> +out_unlock:
> +	rdt_staged_configs_clear();
> +	mutex_unlock(&rdtgroup_mutex);
> +	cpus_read_unlock();
> +
> +	return ret ?: nbytes;
> +}
> +
>  /* rdtgroup information files for one cache resource. */
>  static struct rftype res_common_files[] = {
>  	{
> @@ -2135,9 +2244,10 @@ static struct rftype res_common_files[] = {
>  	},
>  	{
>  		.name		= "io_alloc_cbm",
> -		.mode		= 0444,
> +		.mode		= 0644,
>  		.kf_ops		= &rdtgroup_kf_single_ops,
>  		.seq_show	= resctrl_io_alloc_cbm_show,
> +		.write		= resctrl_io_alloc_cbm_write,
>  	},
>  	{
>  		.name		= "max_threshold_occupancy",

Reinette