"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.

When CDP is enabled, io_alloc routes traffic using the highest CLOSID
associated with the L3CODE resource. To ensure consistent cache allocation
behavior, the L3CODE and L3DATA resources must remain synchronized.
rdtgroup_init_cat() function takes both L3CODE and L3DATA into account when
initializing CBMs for new groups.  The io_alloc feature must maintain the
same behavior, ensuring that the Cache Bit Masks (CBMs) for both L3CODE and
L3DATA are updated together.

Enable users to modify io_alloc CBMs (Capacity Bit Masks) via the
io_alloc_cbm resctrl file when io_alloc is enabled.

Signed-off-by: Babu Moger <babu.moger@amd.com>
---
v8: Updated changelog.
    Moved resctrl_io_alloc_parse_line() and resctrl_io_alloc_cbm_write() to
    fs/resctrl/ctrlmondata.c.
    Added resctrl_arch_get_cdp_enabled() check inside resctrl_io_alloc_parse_line().
    Made parse_cbm() static again as everything moved to ctrlmondata.c.

v7: Updated changelog.
    Updated CBMs for both CDP_DATA and CDP_CODE when CDP is enabled.

v6: Updated the user doc restctr.doc for minor texts.
    Changed the subject to fs/resctrl.

v5: Changes due to FS/ARCH code restructure. The files monitor.c/rdtgroup.c
    have been split between FS and ARCH directories.
    Changed the code to access the CBMs via either L3CODE or L3DATA resources.

v4: Removed resctrl_io_alloc_parse_cbm and called parse_cbm() directly.

v3: Minor changes due to changes in resctrl_arch_get_io_alloc_enabled()
    and resctrl_io_alloc_closid_get().
    Taken care of handling the CBM update when CDP is enabled.
    Updated the commit log to make it generic.

v2: Added more generic text in documentation.
---
 Documentation/filesystems/resctrl.rst |  8 +++
 fs/resctrl/ctrlmondata.c              | 97 +++++++++++++++++++++++++++
 fs/resctrl/internal.h                 |  3 +
 fs/resctrl/rdtgroup.c                 |  3 +-
 4 files changed, 110 insertions(+), 1 deletion(-)

diff --git a/Documentation/filesystems/resctrl.rst b/Documentation/filesystems/resctrl.rst
index 3002f7fdb2fe..d955e8525af0 100644
--- a/Documentation/filesystems/resctrl.rst
+++ b/Documentation/filesystems/resctrl.rst
@@ -187,6 +187,14 @@ 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 641094aac322..1f69117f96f8 100644
--- a/fs/resctrl/ctrlmondata.c
+++ b/fs/resctrl/ctrlmondata.c
@@ -858,3 +858,100 @@ int resctrl_io_alloc_cbm_show(struct kernfs_open_file *of, struct seq_file *seq,
 	cpus_read_unlock();
 	return ret;
 }
+
+static int resctrl_io_alloc_parse_line(char *line,  struct rdt_resource *r,
+				       struct resctrl_schema *s, u32 closid)
+{
+	enum resctrl_conf_type peer_type;
+	struct resctrl_schema *peer_s;
+	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;
+			/*
+			 * When CDP is enabled, update the schema for both CDP_DATA
+			 * and CDP_CODE.
+			 */
+			if (resctrl_arch_get_cdp_enabled(r->rid)) {
+				peer_type = resctrl_peer_type(s->conf_type);
+				peer_s = resctrl_get_schema(peer_type);
+				if (parse_cbm(&data, peer_s, d))
+					return -EINVAL;
+			}
+			goto next;
+		}
+	}
+
+	return -EINVAL;
+}
+
+ssize_t resctrl_io_alloc_cbm_write(struct kernfs_open_file *of, char *buf,
+				   size_t nbytes, loff_t off)
+{
+	struct resctrl_schema *s = rdt_kn_parent_priv(of->kn);
+	struct rdt_resource *r = s->res;
+	u32 io_alloc_closid;
+	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);
+
+	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;
+		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 = -ENODEV;
+		goto out_unlock;
+	}
+
+	io_alloc_closid = resctrl_io_alloc_closid(r);
+
+	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;
+}
diff --git a/fs/resctrl/internal.h b/fs/resctrl/internal.h
index 49934cd3dc40..5467c3ad1b6d 100644
--- a/fs/resctrl/internal.h
+++ b/fs/resctrl/internal.h
@@ -392,6 +392,9 @@ ssize_t resctrl_io_alloc_write(struct kernfs_open_file *of, char *buf,
 int resctrl_io_alloc_cbm_show(struct kernfs_open_file *of, struct seq_file *seq,
 			      void *v);
 
+ssize_t resctrl_io_alloc_cbm_write(struct kernfs_open_file *of, char *buf,
+				   size_t nbytes, loff_t off);
+
 const char *rdtgroup_name_by_closid(int closid);
 
 #ifdef CONFIG_RESCTRL_FS_PSEUDO_LOCK
diff --git a/fs/resctrl/rdtgroup.c b/fs/resctrl/rdtgroup.c
index 6af8ff6c8385..a3ab2851c6da 100644
--- a/fs/resctrl/rdtgroup.c
+++ b/fs/resctrl/rdtgroup.c
@@ -1919,9 +1919,10 @@ 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",
-- 
2.34.1

Hi Babu,

On 8/5/25 4:30 PM, 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.
> 
> When CDP is enabled, io_alloc routes traffic using the highest CLOSID
> associated with the L3CODE resource. To ensure consistent cache allocation
> behavior, the L3CODE and L3DATA resources must remain synchronized.
> rdtgroup_init_cat() function takes both L3CODE and L3DATA into account when
> initializing CBMs for new groups.  The io_alloc feature must maintain the
> same behavior, ensuring that the Cache Bit Masks (CBMs) for both L3CODE and
> L3DATA are updated together.

Please rework this copy&pasted text also and make specific to what this
patch actually does.

> Enable users to modify io_alloc CBMs (Capacity Bit Masks) via the
> io_alloc_cbm resctrl file when io_alloc is enabled.

Here the changelog can provide overview of what is done by this patch
when a user provides a new CBM. This can include that a CBM provided
to CDP enabled resource will copy the CBM to the CDP peer.

> 
> Signed-off-by: Babu Moger <babu.moger@amd.com>
> ---



> ---
>  Documentation/filesystems/resctrl.rst |  8 +++
>  fs/resctrl/ctrlmondata.c              | 97 +++++++++++++++++++++++++++
>  fs/resctrl/internal.h                 |  3 +
>  fs/resctrl/rdtgroup.c                 |  3 +-
>  4 files changed, 110 insertions(+), 1 deletion(-)
> 
> diff --git a/Documentation/filesystems/resctrl.rst b/Documentation/filesystems/resctrl.rst
> index 3002f7fdb2fe..d955e8525af0 100644
> --- a/Documentation/filesystems/resctrl.rst
> +++ b/Documentation/filesystems/resctrl.rst
> @@ -187,6 +187,14 @@ 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

It may be useful to demonstrate syntax when more than one CBM is modified.

> +			# 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 641094aac322..1f69117f96f8 100644
> --- a/fs/resctrl/ctrlmondata.c
> +++ b/fs/resctrl/ctrlmondata.c
> @@ -858,3 +858,100 @@ int resctrl_io_alloc_cbm_show(struct kernfs_open_file *of, struct seq_file *seq,
>  	cpus_read_unlock();
>  	return ret;
>  }
> +
> +static int resctrl_io_alloc_parse_line(char *line,  struct rdt_resource *r,
> +				       struct resctrl_schema *s, u32 closid)
> +{
> +	enum resctrl_conf_type peer_type;
> +	struct resctrl_schema *peer_s;
> +	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;
> +			/*
> +			 * When CDP is enabled, update the schema for both CDP_DATA
> +			 * and CDP_CODE.
> +			 */
> +			if (resctrl_arch_get_cdp_enabled(r->rid)) {
> +				peer_type = resctrl_peer_type(s->conf_type);
> +				peer_s = resctrl_get_schema(peer_type);
> +				if (parse_cbm(&data, peer_s, d))
> +					return -EINVAL;

CBM is still parsed twice. As I mentioned in v7 the parsing only need to be done
once and then the resulting CBM can be copied to CDP peer.
https://lore.kernel.org/lkml/82045638-2b26-4682-9374-1c3e400a580a@intel.com/

> +			}
> +			goto next;
> +		}
> +	}
> +
> +	return -EINVAL;
> +}
> +
> +ssize_t resctrl_io_alloc_cbm_write(struct kernfs_open_file *of, char *buf,
> +				   size_t nbytes, loff_t off)
> +{
> +	struct resctrl_schema *s = rdt_kn_parent_priv(of->kn);
> +	struct rdt_resource *r = s->res;
> +	u32 io_alloc_closid;
> +	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);
> +
> +	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;
> +		goto out_unlock;
> +	}
> +
> +	rdt_last_cmd_clear();

Unnecessary rdt_last_cmd_clear().

> +	rdt_staged_configs_clear();

Placement of this can be improved by putting it closer to the code that
populates the staged configs. That is, just before resctrl_io_alloc_parse_line().
The flow is not symmetrical in that the out_unlock exit code always
clears the buffer whether it was used or not. I think it will be easier to
understand if the out_unlock *only* unlocks the locks and there is a new
goto label, for example, "out_clear_configs" that calls rdt_staged_configs_clear()
and is used after resctrl_io_alloc_parse_line().

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

Reinette

Hi Reinette,

On 8/7/25 20:53, Reinette Chatre wrote:
> Hi Babu,
> 
> On 8/5/25 4:30 PM, 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.
>>
>> When CDP is enabled, io_alloc routes traffic using the highest CLOSID
>> associated with the L3CODE resource. To ensure consistent cache allocation
>> behavior, the L3CODE and L3DATA resources must remain synchronized.
>> rdtgroup_init_cat() function takes both L3CODE and L3DATA into account when
>> initializing CBMs for new groups.  The io_alloc feature must maintain the
>> same behavior, ensuring that the Cache Bit Masks (CBMs) for both L3CODE and
>> L3DATA are updated together.
> 
> Please rework this copy&pasted text also and make specific to what this
> patch actually does.

Sure.

> 
>> Enable users to modify io_alloc CBMs (Capacity Bit Masks) via the
>> io_alloc_cbm resctrl file when io_alloc is enabled.
> 
> Here the changelog can provide overview of what is done by this patch
> when a user provides a new CBM. This can include that a CBM provided
> to CDP enabled resource will copy the CBM to the CDP peer.

Sure.

> 
>>
>> Signed-off-by: Babu Moger <babu.moger@amd.com>
>> ---
> 
> 
> 
>> ---
>>  Documentation/filesystems/resctrl.rst |  8 +++
>>  fs/resctrl/ctrlmondata.c              | 97 +++++++++++++++++++++++++++
>>  fs/resctrl/internal.h                 |  3 +
>>  fs/resctrl/rdtgroup.c                 |  3 +-
>>  4 files changed, 110 insertions(+), 1 deletion(-)
>>
>> diff --git a/Documentation/filesystems/resctrl.rst b/Documentation/filesystems/resctrl.rst
>> index 3002f7fdb2fe..d955e8525af0 100644
>> --- a/Documentation/filesystems/resctrl.rst
>> +++ b/Documentation/filesystems/resctrl.rst
>> @@ -187,6 +187,14 @@ 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
> 
> It may be useful to demonstrate syntax when more than one CBM is modified.

Sure.

> 
>> +			# 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 641094aac322..1f69117f96f8 100644
>> --- a/fs/resctrl/ctrlmondata.c
>> +++ b/fs/resctrl/ctrlmondata.c
>> @@ -858,3 +858,100 @@ int resctrl_io_alloc_cbm_show(struct kernfs_open_file *of, struct seq_file *seq,
>>  	cpus_read_unlock();
>>  	return ret;
>>  }
>> +
>> +static int resctrl_io_alloc_parse_line(char *line,  struct rdt_resource *r,
>> +				       struct resctrl_schema *s, u32 closid)
>> +{
>> +	enum resctrl_conf_type peer_type;
>> +	struct resctrl_schema *peer_s;
>> +	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;
>> +			/*
>> +			 * When CDP is enabled, update the schema for both CDP_DATA
>> +			 * and CDP_CODE.
>> +			 */
>> +			if (resctrl_arch_get_cdp_enabled(r->rid)) {
>> +				peer_type = resctrl_peer_type(s->conf_type);
>> +				peer_s = resctrl_get_schema(peer_type);
>> +				if (parse_cbm(&data, peer_s, d))
>> +					return -EINVAL;
> 
> CBM is still parsed twice. As I mentioned in v7 the parsing only need to be done
> once and then the resulting CBM can be copied to CDP peer.
> https://lore.kernel.org/lkml/82045638-2b26-4682-9374-1c3e400a580a@intel.com/

My bad.  Simplified now to copy the staged_config from source to its peer.

peer_type = resctrl_peer_type(s->conf_type);
memcpy(&d->staged_config[peer_type],
&d->staged_config[s->conf_type],
sizeof(*d->staged_config));



> 
>> +			}
>> +			goto next;
>> +		}
>> +	}
>> +
>> +	return -EINVAL;
>> +}
>> +
>> +ssize_t resctrl_io_alloc_cbm_write(struct kernfs_open_file *of, char *buf,
>> +				   size_t nbytes, loff_t off)
>> +{
>> +	struct resctrl_schema *s = rdt_kn_parent_priv(of->kn);
>> +	struct rdt_resource *r = s->res;
>> +	u32 io_alloc_closid;
>> +	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);
>> +
>> +	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;
>> +		goto out_unlock;
>> +	}
>> +
>> +	rdt_last_cmd_clear();
> 
> Unnecessary rdt_last_cmd_clear().

Removed it.

> 
>> +	rdt_staged_configs_clear();
> 
> Placement of this can be improved by putting it closer to the code that
> populates the staged configs. That is, just before resctrl_io_alloc_parse_line().
> The flow is not symmetrical in that the out_unlock exit code always
> clears the buffer whether it was used or not. I think it will be easier to
> understand if the out_unlock *only* unlocks the locks and there is a new
> goto label, for example, "out_clear_configs" that calls rdt_staged_configs_clear()
> and is used after resctrl_io_alloc_parse_line().

Yes. Sound good.

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

-- 
Thanks
Babu Moger