Resctrl subsystem can support two monitoring modes, 'mbm_cntr_assign' or
'default'. In mbm_cntr_assign, monitoring event can only accumulate data
while it is backed by a hardware counter. In 'default' mode, resctrl
assumes there is a hardware counter for each event within every CTRL_MON
and MON group.

Introduce interface to switch between mbm_cntr_assign and default modes.

$ cat /sys/fs/resctrl/info/L3_MON/mbm_assign_mode
[mbm_cntr_assign]
default

To enable the "mbm_cntr_assign" mode:
$ echo "mbm_cntr_assign" > /sys/fs/resctrl/info/L3_MON/mbm_assign_mode

To enable the default monitoring mode:
$ echo "default" > /sys/fs/resctrl/info/L3_MON/mbm_assign_mode

MBM event counters are automatically reset as part of changing the mode.
Clear both architectural and non-architectural event states to prevent
overflow conditions during the next event read.

Signed-off-by: Babu Moger <babu.moger@amd.com>
---
v11: Changed the name of the function rdtgroup_mbm_assign_mode_write() to
     resctrl_mbm_assign_mode_write().
     Rewrote the commit message with context.
     Added few more details in resctrl.rst about mbm_cntr_assign mode.
     Re-arranged the text in resctrl.rst file.

v10: The call mbm_cntr_reset() has been moved to earlier patch.
     Minor documentation update.

v9: Fixed extra spaces in user documentation.
    Fixed problem changing the mode to mbm_cntr_assign mode when it is
    not supported. Added extra checks to detect if systems supports it.
    Used the rdtgroup_cntr_id_init to initialize cntr_id.

v8: Reset the internal counters after mbm_cntr_assign mode is changed.
    Renamed rdtgroup_mbm_cntr_reset() to mbm_cntr_reset()
    Updated the documentation to make text generic.

v7: Changed the interface name to mbm_assign_mode.
    Removed the references of ABMC.
    Added the changes to reset global and domain bitmaps.
    Added the changes to reset rmid.

v6: Changed the mode name to mbm_cntr_assign.
    Moved all the FS related code here.
    Added changes to reset mbm_cntr_map and resctrl group counters.

v5: Change log and mode description text correction.

v4: Minor commit text changes. Keep the default to ABMC when supported.
    Fixed comments to reflect changed interface "mbm_mode".

v3: New patch to address the review comments from upstream.
---
 Documentation/arch/x86/resctrl.rst     | 25 ++++++++++++-
 arch/x86/kernel/cpu/resctrl/rdtgroup.c | 50 +++++++++++++++++++++++++-
 2 files changed, 73 insertions(+), 2 deletions(-)

diff --git a/Documentation/arch/x86/resctrl.rst b/Documentation/arch/x86/resctrl.rst
index 072b15550ff7..5d18c4c8bc48 100644
--- a/Documentation/arch/x86/resctrl.rst
+++ b/Documentation/arch/x86/resctrl.rst
@@ -259,7 +259,10 @@ with the following files:
 
 "mbm_assign_mode":
 	Reports the list of monitoring modes supported. The enclosed brackets
-	indicate which mode is enabled.
+	indicate which mode is enabled. The MBM events (mbm_total_bytes and/or
+	mbm_local_bytes) associated with counters may reset when "mbm_assign_mode"
+	is changed.
+
 	::
 
 	  # cat /sys/fs/resctrl/info/L3_MON/mbm_assign_mode
@@ -275,6 +278,16 @@ with the following files:
 	available is described in the "num_mbm_cntrs" file. Changing the mode
 	may cause all counters on a resource to reset.
 
+	Moving to mbm_cntr_assign mode require users to assign the counters to
+	the events. Otherwise, the MBM event counters will return "Unassigned"
+	when read.
+
+	The mode is beneficial for AMD platforms that support more CTRL_MON
+	and MON groups than available hardware counters. By default, this
+	feature is enabled on AMD platforms with the ABMC (Assignable Bandwidth
+	Monitoring Counters) capability, ensuring counters remain assigned even
+	when the corresponding RMID is not actively used by any processor.
+
 	"default":
 
 	In default mode, resctrl assumes there is a hardware counter for each
@@ -283,6 +296,16 @@ with the following files:
 	"mbm_total_bytes" or "mbm_local_bytes" will report 'Unavailable' if
 	there is no counter associated with that event.
 
+	* To enable "mbm_cntr_assign" mode:
+	  ::
+
+	    # echo "mbm_cntr_assign" > /sys/fs/resctrl/info/L3_MON/mbm_assign_mode
+
+	* To enable default monitoring mode:
+	  ::
+
+	    # echo "default" > /sys/fs/resctrl/info/L3_MON/mbm_assign_mode
+
 "num_mbm_cntrs":
 	The number of monitoring counters available for assignment when the
 	system supports mbm_cntr_assign mode.
diff --git a/arch/x86/kernel/cpu/resctrl/rdtgroup.c b/arch/x86/kernel/cpu/resctrl/rdtgroup.c
index f61f0cd032ef..6922173c4f8f 100644
--- a/arch/x86/kernel/cpu/resctrl/rdtgroup.c
+++ b/arch/x86/kernel/cpu/resctrl/rdtgroup.c
@@ -928,6 +928,53 @@ static int resctrl_available_mbm_cntrs_show(struct kernfs_open_file *of,
 	return ret;
 }
 
+static ssize_t resctrl_mbm_assign_mode_write(struct kernfs_open_file *of,
+					     char *buf, size_t nbytes, loff_t off)
+{
+	struct rdt_resource *r = of->kn->parent->priv;
+	int ret = 0;
+	bool enable;
+
+	/* 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 (!strcmp(buf, "default")) {
+		enable = 0;
+	} else if (!strcmp(buf, "mbm_cntr_assign")) {
+		if (r->mon.mbm_cntr_assignable) {
+			enable = 1;
+		} else {
+			ret = -EINVAL;
+			rdt_last_cmd_puts("mbm_cntr_assign mode is not supported\n");
+			goto write_exit;
+		}
+	} else {
+		ret = -EINVAL;
+		rdt_last_cmd_puts("Unsupported assign mode\n");
+		goto write_exit;
+	}
+
+	if (enable != resctrl_arch_mbm_cntr_assign_enabled(r)) {
+		ret = resctrl_arch_mbm_cntr_assign_set(r, enable);
+		if (!ret)
+			mbm_cntr_reset(r);
+	}
+
+write_exit:
+	mutex_unlock(&rdtgroup_mutex);
+	cpus_read_unlock();
+
+	return ret ?: nbytes;
+}
+
 #ifdef CONFIG_PROC_CPU_RESCTRL
 
 /*
@@ -1945,9 +1992,10 @@ static struct rftype res_common_files[] = {
 	},
 	{
 		.name		= "mbm_assign_mode",
-		.mode		= 0444,
+		.mode		= 0644,
 		.kf_ops		= &rdtgroup_kf_single_ops,
 		.seq_show	= resctrl_mbm_assign_mode_show,
+		.write		= resctrl_mbm_assign_mode_write,
 		.fflags		= RFTYPE_MON_INFO,
 	},
 	{
-- 
2.34.1

Hi Babu,

On 1/22/25 12:20 PM, Babu Moger wrote:
> Resctrl subsystem can support two monitoring modes, 'mbm_cntr_assign' or
> 'default'. In mbm_cntr_assign, monitoring event can only accumulate data
> while it is backed by a hardware counter. In 'default' mode, resctrl
> assumes there is a hardware counter for each event within every CTRL_MON
> and MON group.
> 
> Introduce interface to switch between mbm_cntr_assign and default modes.
> 
> $ cat /sys/fs/resctrl/info/L3_MON/mbm_assign_mode
> [mbm_cntr_assign]
> default
> 
> To enable the "mbm_cntr_assign" mode:
> $ echo "mbm_cntr_assign" > /sys/fs/resctrl/info/L3_MON/mbm_assign_mode
> 
> To enable the default monitoring mode:
> $ echo "default" > /sys/fs/resctrl/info/L3_MON/mbm_assign_mode
> 
> MBM event counters are automatically reset as part of changing the mode.
> Clear both architectural and non-architectural event states to prevent
> overflow conditions during the next event read.
> 
> Signed-off-by: Babu Moger <babu.moger@amd.com>
> ---


> ---
>  Documentation/arch/x86/resctrl.rst     | 25 ++++++++++++-
>  arch/x86/kernel/cpu/resctrl/rdtgroup.c | 50 +++++++++++++++++++++++++-
>  2 files changed, 73 insertions(+), 2 deletions(-)
> 
> diff --git a/Documentation/arch/x86/resctrl.rst b/Documentation/arch/x86/resctrl.rst
> index 072b15550ff7..5d18c4c8bc48 100644
> --- a/Documentation/arch/x86/resctrl.rst
> +++ b/Documentation/arch/x86/resctrl.rst
> @@ -259,7 +259,10 @@ with the following files:
>  
>  "mbm_assign_mode":
>  	Reports the list of monitoring modes supported. The enclosed brackets
> -	indicate which mode is enabled.
> +	indicate which mode is enabled. The MBM events (mbm_total_bytes and/or
> +	mbm_local_bytes) associated with counters may reset when "mbm_assign_mode"
> +	is changed.
> +
>  	::
>  
>  	  # cat /sys/fs/resctrl/info/L3_MON/mbm_assign_mode
> @@ -275,6 +278,16 @@ with the following files:
>  	available is described in the "num_mbm_cntrs" file. Changing the mode
>  	may cause all counters on a resource to reset.
>  
> +	Moving to mbm_cntr_assign mode require users to assign the counters to
> +	the events. Otherwise, the MBM event counters will return "Unassigned"
> +	when read.

Again ... please be consistent in using single or double quotes for information
returned from file.

> +
> +	The mode is beneficial for AMD platforms that support more CTRL_MON
> +	and MON groups than available hardware counters. By default, this
> +	feature is enabled on AMD platforms with the ABMC (Assignable Bandwidth
> +	Monitoring Counters) capability, ensuring counters remain assigned even
> +	when the corresponding RMID is not actively used by any processor.
> +
>  	"default":
>  
>  	In default mode, resctrl assumes there is a hardware counter for each
> @@ -283,6 +296,16 @@ with the following files:
>  	"mbm_total_bytes" or "mbm_local_bytes" will report 'Unavailable' if
>  	there is no counter associated with that event.
>  
> +	* To enable "mbm_cntr_assign" mode:
> +	  ::
> +
> +	    # echo "mbm_cntr_assign" > /sys/fs/resctrl/info/L3_MON/mbm_assign_mode
> +
> +	* To enable default monitoring mode:
> +	  ::
> +
> +	    # echo "default" > /sys/fs/resctrl/info/L3_MON/mbm_assign_mode
> +

Please be consistent in the documentation.

To enable "mbm_cntr_assign" mode:
To enable "default" mode:
or
To enable "mbm_cntr_assign" monitoring mode:
To enable "default" monitoring mode:
or 
...?



>  "num_mbm_cntrs":
>  	The number of monitoring counters available for assignment when the
>  	system supports mbm_cntr_assign mode.
> diff --git a/arch/x86/kernel/cpu/resctrl/rdtgroup.c b/arch/x86/kernel/cpu/resctrl/rdtgroup.c
> index f61f0cd032ef..6922173c4f8f 100644
> --- a/arch/x86/kernel/cpu/resctrl/rdtgroup.c
> +++ b/arch/x86/kernel/cpu/resctrl/rdtgroup.c
> @@ -928,6 +928,53 @@ static int resctrl_available_mbm_cntrs_show(struct kernfs_open_file *of,
>  	return ret;
>  }
>  
> +static ssize_t resctrl_mbm_assign_mode_write(struct kernfs_open_file *of,
> +					     char *buf, size_t nbytes, loff_t off)
> +{
> +	struct rdt_resource *r = of->kn->parent->priv;
> +	int ret = 0;
> +	bool enable;
> +
> +	/* 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 (!strcmp(buf, "default")) {
> +		enable = 0;
> +	} else if (!strcmp(buf, "mbm_cntr_assign")) {
> +		if (r->mon.mbm_cntr_assignable) {
> +			enable = 1;
> +		} else {
> +			ret = -EINVAL;
> +			rdt_last_cmd_puts("mbm_cntr_assign mode is not supported\n");
> +			goto write_exit;
> +		}
> +	} else {
> +		ret = -EINVAL;
> +		rdt_last_cmd_puts("Unsupported assign mode\n");
> +		goto write_exit;
> +	}
> +
> +	if (enable != resctrl_arch_mbm_cntr_assign_enabled(r)) {
> +		ret = resctrl_arch_mbm_cntr_assign_set(r, enable);
> +		if (!ret)
> +			mbm_cntr_reset(r);

The following APIs interact with the MBM assignable counters:

mbm_cntr_alloc()
mbm_cntr_get()
mbm_cntr_free()

mbm_cntr_reset() appears to be related but does significantly more
than interact with the MBM assignable counters and that creates a
confusing API.

How about introducing mbm_cntr_free_all() that _only_ releases all
MBM assignable counters and match with mbm_cntr_free() that releases
a single MBM assignable counter? mbm_cntr_free_all() lives with the
other functions operating on MBM assignable counters, thus not
hiding its functionality in other parts of resctrl.

This series open codes reset of non-architectural state in two places,
within mbm_cntr_reset() and within mbm_config_write_domain(). That
can be turned into a new helper that only resets architectural state,
for example resctrl_reset_rmid_all() to match existing
resctrl_arch_reset_rmid_all().

resctrl_arch_mbm_cntr_assign_set() can also reset any architectural
state leaving mbm_cntr_free_all() and resctrl_reset_rmid_all() to be called
here and from within mbm_config_write_domain().

What do you think?

> +	}
> +
> +write_exit:
> +	mutex_unlock(&rdtgroup_mutex);
> +	cpus_read_unlock();
> +
> +	return ret ?: nbytes;
> +}
> +
>  #ifdef CONFIG_PROC_CPU_RESCTRL
>  
>  /*
> @@ -1945,9 +1992,10 @@ static struct rftype res_common_files[] = {
>  	},
>  	{
>  		.name		= "mbm_assign_mode",
> -		.mode		= 0444,
> +		.mode		= 0644,
>  		.kf_ops		= &rdtgroup_kf_single_ops,
>  		.seq_show	= resctrl_mbm_assign_mode_show,
> +		.write		= resctrl_mbm_assign_mode_write,
>  		.fflags		= RFTYPE_MON_INFO,
>  	},
>  	{

Reinette

Hi Reinette,

On 2/6/25 12:05, Reinette Chatre wrote:
> Hi Babu,
> 
> On 1/22/25 12:20 PM, Babu Moger wrote:
>> Resctrl subsystem can support two monitoring modes, 'mbm_cntr_assign' or
>> 'default'. In mbm_cntr_assign, monitoring event can only accumulate data
>> while it is backed by a hardware counter. In 'default' mode, resctrl
>> assumes there is a hardware counter for each event within every CTRL_MON
>> and MON group.
>>
>> Introduce interface to switch between mbm_cntr_assign and default modes.
>>
>> $ cat /sys/fs/resctrl/info/L3_MON/mbm_assign_mode
>> [mbm_cntr_assign]
>> default
>>
>> To enable the "mbm_cntr_assign" mode:
>> $ echo "mbm_cntr_assign" > /sys/fs/resctrl/info/L3_MON/mbm_assign_mode
>>
>> To enable the default monitoring mode:
>> $ echo "default" > /sys/fs/resctrl/info/L3_MON/mbm_assign_mode
>>
>> MBM event counters are automatically reset as part of changing the mode.
>> Clear both architectural and non-architectural event states to prevent
>> overflow conditions during the next event read.
>>
>> Signed-off-by: Babu Moger <babu.moger@amd.com>
>> ---
> 
> 
>> ---
>>  Documentation/arch/x86/resctrl.rst     | 25 ++++++++++++-
>>  arch/x86/kernel/cpu/resctrl/rdtgroup.c | 50 +++++++++++++++++++++++++-
>>  2 files changed, 73 insertions(+), 2 deletions(-)
>>
>> diff --git a/Documentation/arch/x86/resctrl.rst b/Documentation/arch/x86/resctrl.rst
>> index 072b15550ff7..5d18c4c8bc48 100644
>> --- a/Documentation/arch/x86/resctrl.rst
>> +++ b/Documentation/arch/x86/resctrl.rst
>> @@ -259,7 +259,10 @@ with the following files:
>>  
>>  "mbm_assign_mode":
>>  	Reports the list of monitoring modes supported. The enclosed brackets
>> -	indicate which mode is enabled.
>> +	indicate which mode is enabled. The MBM events (mbm_total_bytes and/or
>> +	mbm_local_bytes) associated with counters may reset when "mbm_assign_mode"
>> +	is changed.
>> +
>>  	::
>>  
>>  	  # cat /sys/fs/resctrl/info/L3_MON/mbm_assign_mode
>> @@ -275,6 +278,16 @@ with the following files:
>>  	available is described in the "num_mbm_cntrs" file. Changing the mode
>>  	may cause all counters on a resource to reset.
>>  
>> +	Moving to mbm_cntr_assign mode require users to assign the counters to
>> +	the events. Otherwise, the MBM event counters will return "Unassigned"
>> +	when read.
> 
> Again ... please be consistent in using single or double quotes for information
> returned from file.

ok. Will change it to 'Unassigned'.

> 
>> +
>> +	The mode is beneficial for AMD platforms that support more CTRL_MON
>> +	and MON groups than available hardware counters. By default, this
>> +	feature is enabled on AMD platforms with the ABMC (Assignable Bandwidth
>> +	Monitoring Counters) capability, ensuring counters remain assigned even
>> +	when the corresponding RMID is not actively used by any processor.
>> +
>>  	"default":
>>  
>>  	In default mode, resctrl assumes there is a hardware counter for each
>> @@ -283,6 +296,16 @@ with the following files:
>>  	"mbm_total_bytes" or "mbm_local_bytes" will report 'Unavailable' if
>>  	there is no counter associated with that event.
>>  
>> +	* To enable "mbm_cntr_assign" mode:
>> +	  ::
>> +
>> +	    # echo "mbm_cntr_assign" > /sys/fs/resctrl/info/L3_MON/mbm_assign_mode
>> +
>> +	* To enable default monitoring mode:
>> +	  ::
>> +
>> +	    # echo "default" > /sys/fs/resctrl/info/L3_MON/mbm_assign_mode
>> +
> 
> Please be consistent in the documentation.
> 
> To enable "mbm_cntr_assign" mode:
> To enable "default" mode:
> or
> To enable "mbm_cntr_assign" monitoring mode:
> To enable "default" monitoring mode:

This sounds (monitoring mode) better.

> or 
> ...?
> 
> 
> 
>>  "num_mbm_cntrs":
>>  	The number of monitoring counters available for assignment when the
>>  	system supports mbm_cntr_assign mode.
>> diff --git a/arch/x86/kernel/cpu/resctrl/rdtgroup.c b/arch/x86/kernel/cpu/resctrl/rdtgroup.c
>> index f61f0cd032ef..6922173c4f8f 100644
>> --- a/arch/x86/kernel/cpu/resctrl/rdtgroup.c
>> +++ b/arch/x86/kernel/cpu/resctrl/rdtgroup.c
>> @@ -928,6 +928,53 @@ static int resctrl_available_mbm_cntrs_show(struct kernfs_open_file *of,
>>  	return ret;
>>  }
>>  
>> +static ssize_t resctrl_mbm_assign_mode_write(struct kernfs_open_file *of,
>> +					     char *buf, size_t nbytes, loff_t off)
>> +{
>> +	struct rdt_resource *r = of->kn->parent->priv;
>> +	int ret = 0;
>> +	bool enable;
>> +
>> +	/* 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 (!strcmp(buf, "default")) {
>> +		enable = 0;
>> +	} else if (!strcmp(buf, "mbm_cntr_assign")) {
>> +		if (r->mon.mbm_cntr_assignable) {
>> +			enable = 1;
>> +		} else {
>> +			ret = -EINVAL;
>> +			rdt_last_cmd_puts("mbm_cntr_assign mode is not supported\n");
>> +			goto write_exit;
>> +		}
>> +	} else {
>> +		ret = -EINVAL;
>> +		rdt_last_cmd_puts("Unsupported assign mode\n");
>> +		goto write_exit;
>> +	}
>> +
>> +	if (enable != resctrl_arch_mbm_cntr_assign_enabled(r)) {
>> +		ret = resctrl_arch_mbm_cntr_assign_set(r, enable);
>> +		if (!ret)
>> +			mbm_cntr_reset(r);
> 
> The following APIs interact with the MBM assignable counters:
> 
> mbm_cntr_alloc()
> mbm_cntr_get()
> mbm_cntr_free()
> 
> mbm_cntr_reset() appears to be related but does significantly more
> than interact with the MBM assignable counters and that creates a
> confusing API.
> 
> How about introducing mbm_cntr_free_all() that _only_ releases all
> MBM assignable counters and match with mbm_cntr_free() that releases
> a single MBM assignable counter? mbm_cntr_free_all() lives with the
> other functions operating on MBM assignable counters, thus not
> hiding its functionality in other parts of resctrl.
> 
> This series open codes reset of non-architectural state in two places,
> within mbm_cntr_reset() and within mbm_config_write_domain(). That
> can be turned into a new helper that only resets architectural state,
> for example resctrl_reset_rmid_all() to match existing
> resctrl_arch_reset_rmid_all().
> 
> resctrl_arch_mbm_cntr_assign_set() can also reset any architectural
> state leaving mbm_cntr_free_all() and resctrl_reset_rmid_all() to be called
> here and from within mbm_config_write_domain().
> 
> What do you think?

Sounds like a good code separation. It should be fine.
Will let you know if there are any issues.

> 
>> +	}
>> +
>> +write_exit:
>> +	mutex_unlock(&rdtgroup_mutex);
>> +	cpus_read_unlock();
>> +
>> +	return ret ?: nbytes;
>> +}
>> +
>>  #ifdef CONFIG_PROC_CPU_RESCTRL
>>  
>>  /*
>> @@ -1945,9 +1992,10 @@ static struct rftype res_common_files[] = {
>>  	},
>>  	{
>>  		.name		= "mbm_assign_mode",
>> -		.mode		= 0444,
>> +		.mode		= 0644,
>>  		.kf_ops		= &rdtgroup_kf_single_ops,
>>  		.seq_show	= resctrl_mbm_assign_mode_show,
>> +		.write		= resctrl_mbm_assign_mode_write,
>>  		.fflags		= RFTYPE_MON_INFO,
>>  	},
>>  	{
> 
> Reinette
> 

-- 
Thanks
Babu Moger