Message-ID: <de20ecd6-8cb2-4b3b-ba5f-b38f33fe128b@intel.com>
Date: Thu, 17 Jul 2025 21:01:16 -0700
From: Reinette Chatre <reinette.chatre@...el.com>
To: Babu Moger <babu.moger@....com>, <corbet@....net>, <tony.luck@...el.com>,
	<james.morse@....com>, <tglx@...utronix.de>, <mingo@...hat.com>,
	<bp@...en8.de>, <dave.hansen@...ux.intel.com>
CC: <Dave.Martin@....com>, <x86@...nel.org>, <hpa@...or.com>,
	<akpm@...ux-foundation.org>, <paulmck@...nel.org>, <rostedt@...dmis.org>,
	<Neeraj.Upadhyay@....com>, <david@...hat.com>, <arnd@...db.de>,
	<fvdl@...gle.com>, <seanjc@...gle.com>, <jpoimboe@...nel.org>,
	<pawan.kumar.gupta@...ux.intel.com>, <xin@...or.com>,
	<manali.shukla@....com>, <tao1.su@...ux.intel.com>, <sohil.mehta@...el.com>,
	<kai.huang@...el.com>, <xiaoyao.li@...el.com>, <peterz@...radead.org>,
	<xin3.li@...el.com>, <kan.liang@...ux.intel.com>,
	<mario.limonciello@....com>, <thomas.lendacky@....com>, <perry.yuan@....com>,
	<gautham.shenoy@....com>, <chang.seok.bae@...el.com>,
	<linux-doc@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
	<peternewman@...gle.com>, <eranian@...gle.com>
Subject: Re: [PATCH v15 31/34] fs/resctrl: Introduce the interface to modify
 assignments in a group

Hi Babu,

On 7/8/25 3:17 PM, Babu Moger wrote:
> Enable the mbm_l3_assignments resctrl file to be used to modify counter
> assignments of CTRL_MON and MON groups when the "mbm_event" counter
> assignment mode is enabled.
> 
> The assignment modifications are done in the following format:
> <Event>:<Domain id>=<Assignment state>
> 
> Event: A valid MBM event in the
>        /sys/fs/resctrl/info/L3_MON/event_configs directory.
> 
> Domain ID: A valid domain ID. When writing, '*' applies the changes
> 	   to all domains.
> 
> Assignment states:
> 
>     _ : Unassign the counter.

"the counter" -> "a counter" (user cannot control which counter is assigned)

> 
>     e : Assign the counter exclusively.

"the counter" -> "a counter"

> 
> Examples:
> 
> $ cd /sys/fs/resctrl
> $ cat /sys/fs/resctrl/mbm_L3_assignments
>   mbm_total_bytes:0=e;1=e
>   mbm_local_bytes:0=e;1=e
> 
> To unassign the counter associated with the mbm_total_bytes event on
> domain 0:
> 
> $ echo "mbm_total_bytes:0=_" > mbm_L3_assignments
> $ cat /sys/fs/resctrl/mbm_L3_assignments
>   mbm_total_bytes:0=_;1=e
>   mbm_local_bytes:0=e;1=e
> 
> To unassign the counter associated with the mbm_total_bytes event on
> all the domains:
> 
> $ echo "mbm_total_bytes:*=_" > mbm_L3_assignments
> $ cat /sys/fs/resctrl/mbm_L3_assignments
>   mbm_total_bytes:0=_;1=_
>   mbm_local_bytes:0=e;1=e
> 
> Signed-off-by: Babu Moger <babu.moger@....com>
> ---

...

> ---
>  Documentation/filesystems/resctrl.rst | 146 +++++++++++++++++++++++++-
>  fs/resctrl/internal.h                 |   2 +
>  fs/resctrl/monitor.c                  |  18 ++++
>  fs/resctrl/rdtgroup.c                 | 123 +++++++++++++++++++++-
>  4 files changed, 287 insertions(+), 2 deletions(-)
> 
> diff --git a/Documentation/filesystems/resctrl.rst b/Documentation/filesystems/resctrl.rst
> index 4dd1d605d6ad..2b2acb55d8b1 100644
> --- a/Documentation/filesystems/resctrl.rst
> +++ b/Documentation/filesystems/resctrl.rst
> @@ -527,7 +527,8 @@ When the "mba_MBps" mount option is used all CTRL_MON groups will also contain:
>  	Event: A valid MBM event in the
>  	       /sys/fs/resctrl/info/L3_MON/event_configs directory.
>  
> -	Domain ID: A valid domain ID.
> +	Domain ID: A valid domain ID. When writing, '*' applies the changes
> +		   to all the domains.
>  
>  	Assignment states:
>  
> @@ -544,6 +545,34 @@ When the "mba_MBps" mount option is used all CTRL_MON groups will also contain:
>  	   mbm_total_bytes:0=e;1=e
>  	   mbm_local_bytes:0=e;1=e
>  
> +	Assignments can be modified by writing to the interface.
> +
> +	Example:
> +	To unassign the counter associated with the mbm_total_bytes event on domain 0:
> +	::
> +
> +	 # echo "mbm_total_bytes:0=_" > /sys/fs/resctrl/mbm_L3_assignments
> +	 # cat /sys/fs/resctrl/mbm_L3_assignments
> +	   mbm_total_bytes:0=_;1=e
> +	   mbm_local_bytes:0=e;1=e
> +
> +	To unassign the counter associated with the mbm_total_bytes event on all the domains:
> +	::
> +
> +	 # echo "mbm_total_bytes:*=_" > /sys/fs/resctrl/mbm_L3_assignments
> +	 # cat /sys/fs/resctrl/mbm_L3_assignments
> +	   mbm_total_bytes:0=_;1=_
> +	   mbm_local_bytes:0=e;1=e
> +
> +	To assign the counter associated with the mbm_total_bytes event on all domains in

"the counter" -> "a counter" (motivation: user space cannot control which counter is assigned)

> +	exclusive mode:
> +	::
> +
> +	 # echo "mbm_total_bytes:*=e" > /sys/fs/resctrl/mbm_L3_assignments
> +	 # cat /sys/fs/resctrl/mbm_L3_assignments
> +	   mbm_total_bytes:0=e;1=e
> +	   mbm_local_bytes:0=e;1=e
> +
>  Resource allocation rules
>  -------------------------
>  
> @@ -1579,6 +1608,121 @@ View the llc occupancy snapshot::
>    # cat /sys/fs/resctrl/p1/mon_data/mon_L3_00/llc_occupancy
>    11234000
>  
> +
> +Examples on working with mbm_assign_mode
> +========================================
> +
> +a. Check if MBM counter assignment mode is supported.
> +::
> +
> +  #mount -t resctrl resctrl /sys/fs/resctrl/

"#mount" -> "# mount" (please build htmldocs to confirm everything
looks consistent)

> +
> +  # cat /sys/fs/resctrl/info/L3_MON/mbm_assign_mode
> +  [mbm_event]
> +  default
> +
> +The "mbm_event" mode is detected and enabled.
> +
> +b. Check how many assignable counters are supported.
> +::
> +
> +  # cat /sys/fs/resctrl/info/L3_MON/num_mbm_cntrs
> +  0=32;1=32
> +
> +c. Check how many assignable counters are available for assignment in each domain.
> +::
> +
> +  # cat /sys/fs/resctrl/info/L3_MON/available_mbm_cntrs
> +  0=30;1=30
> +
> +d. To list the default group's assign states:

Please note that these steps are inconsistent. Some end with "." and some end with ":"

> +::
> +
> +  # cat /sys/fs/resctrl/mbm_L3_assignments
> +  mbm_total_bytes:0=e;1=e
> +  mbm_local_bytes:0=e;1=e
> +
> +e.  To unassign the counter associated with the mbm_total_bytes event on domain 0:
> +::
> +
> +  # echo "mbm_total_bytes:0=_" > /sys/fs/resctrl/mbm_L3_assignments
> +  # cat /sys/fs/resctrl/mbm_L3_assignments
> +  mbm_total_bytes:0=_;1=e
> +  mbm_local_bytes:0=e;1=e
> +
> +f. To unassign the counter associated with the mbm_total_bytes event on all domains:
> +::
> +
> +  # echo "mbm_total_bytes:*=_" > /sys/fs/resctrl/mbm_L3_assignments
> +  # cat /sys/fs/resctrl/mbm_L3_assignment
> +  mbm_total_bytes:0=_;1=_
> +  mbm_local_bytes:0=e;1=e
> +
> +g. To assign a counter associated with the mbm_total_bytes event on all domains in

ah ... here "a counter" is used.

> +exclusive mode:
> +::
> +
> +  # echo "mbm_total_bytes:*=e" > /sys/fs/resctrl/mbm_L3_assignments
> +  # cat /sys/fs/resctrl/mbm_L3_assignments
> +  mbm_total_bytes:0=e;1=e
> +  mbm_local_bytes:0=e;1=e
> +
> +h. Read the events mbm_total_bytes and mbm_local_bytes of the default group. There is
> +no change in reading the events with the assignment.  If the event is unassigned when
> +reading, then the read will come back as "Unassigned".

Since returning "Unassigned" can be complicated, the associated description should
probably just be done once in the doc. I expect this will be in the "mon_data" section.

> +::
> +
> +  # cat /sys/fs/resctrl/mon_data/mon_L3_00/mbm_total_bytes
> +  779247936
> +  # cat /sys/fs/resctrl/mon_data/mon_L3_00/mbm_local_bytes
> +  765207488
> +
> +i. Check the default event configurations.

Drop "default" (there are only these event configurations)

> +::
> +
> +  # cat /sys/fs/resctrl/info/L3_MON/event_configs/mbm_total_bytes/event_filter
> +  local_reads,remote_reads,local_non_temporal_writes,remote_non_temporal_writes,
> +  local_reads_slow_memory,remote_reads_slow_memory,dirty_victim_writes_all
> +
> +  # cat /sys/fs/resctrl/info/L3_MON/event_configs/mbm_local_bytes/event_filter
> +  local_reads,local_non_temporal_writes,local_reads_slow_memory
> +
> +j. Change the event configuration for mbm_local_bytes.
> +::
> +
> +  # echo "local_reads, local_non_temporal_writes, local_reads_slow_memory, remote_reads" >
> +  /sys/fs/resctrl/info/L3_MON/counter_configs/mbm_local_bytes/event_filter

"counter_configs" -> "event_configs" (this was also an issue in previous series, please
use grep to ensure all are fixed)

> +
> +  # cat /sys/fs/resctrl/info/L3_MON/counter_configs/mbm_local_bytes/event_filter

"counter_configs" -> "event_configs"

> +  local_reads,local_non_temporal_writes,local_reads_slow_memory,remote_reads
> +
> +This will update all (across all domains of all monitor groups) counter assignments
> +associated with the mbm_local_bytes event.
> +
> +k. Now read the local event again. The first read may come back with "Unavailable"
> +status. The subsequent read of mbm_local_bytes will display the current value.
> +::
> +
> +  # cat /sys/fs/resctrl/mon_data/mon_L3_00/mbm_local_bytes
> +  Unavailable
> +  # cat /sys/fs/resctrl/mon_data/mon_L3_00/mbm_local_bytes
> +  314101
> +
> +l. Users have the option to go back to 'default' mbm_assign_mode if required. This can be
> +done using the following command. Note that switching the mbm_assign_mode may reset all
> +the MBM counters (and thus all MBM events) of all the resctrl groups.
> +::
> +
> +  # echo "default" > /sys/fs/resctrl/info/L3_MON/mbm_assign_mode
> +  # cat /sys/fs/resctrl/info/L3_MON/mbm_assign_mode
> +  mbm_event
> +  [default]
> +
> +m. Unmount the resctrl

"Unmount the resctrl" -> "Unmount resctrl" or "Unmount the resctrl filesystem"?

> +::
> +
> +  #umount /sys/fs/resctrl/

"#umount" -> "# umount"

> +
>  Intel RDT Errata
>  ================
>  
> diff --git a/fs/resctrl/internal.h b/fs/resctrl/internal.h
> index b42890fd937a..9881674909f2 100644
> --- a/fs/resctrl/internal.h
> +++ b/fs/resctrl/internal.h
> @@ -403,6 +403,8 @@ bool closid_allocated(unsigned int closid);
>  
>  int resctrl_find_cleanest_closid(void);
>  
> +struct mon_evt *mbm_get_mon_event_by_name(struct rdt_resource *r, char *name);
> +
>  int rdtgroup_assign_cntr_event(struct rdt_mon_domain *d, struct rdtgroup *rdtgrp,
>  			       struct mon_evt *mevt);
>  void rdtgroup_unassign_cntr_event(struct rdt_mon_domain *d, struct rdtgroup *rdtgrp,
> diff --git a/fs/resctrl/monitor.c b/fs/resctrl/monitor.c
> index e30a867c00bb..61419849b257 100644
> --- a/fs/resctrl/monitor.c
> +++ b/fs/resctrl/monitor.c
> @@ -1220,3 +1220,21 @@ void resctrl_update_cntr_allrdtgrp(struct mon_evt *mevt)
>  			rdtgroup_update_cntr_event(r, crgrp, mevt->evtid);
>  	}
>  }
> +
> +/*
> + * mbm_get_mon_event_by_name() - Return the mon_evt entry for the matching
> + * event name.
> + */
> +struct mon_evt *mbm_get_mon_event_by_name(struct rdt_resource *r, char *name)
> +{
> +	struct mon_evt *mevt;
> +
> +	for_each_mon_event(mevt) {
> +		if (mevt->rid == r->rid && mevt->enabled &&
> +		    resctrl_is_mbm_event(mevt->evtid) &&
> +		    !strcmp(mevt->name, name))
> +			return mevt;
> +	}
> +
> +	return NULL;
> +}
> diff --git a/fs/resctrl/rdtgroup.c b/fs/resctrl/rdtgroup.c
> index dc108c5db298..b26baca389bb 100644
> --- a/fs/resctrl/rdtgroup.c
> +++ b/fs/resctrl/rdtgroup.c
> @@ -2071,6 +2071,126 @@ static int mbm_L3_assignments_show(struct kernfs_open_file *of, struct seq_file
>  	return ret;
>  }
>  
> +static int rdtgroup_modify_assign_state(char *assign, struct rdt_mon_domain *d,

Please move to monitor.c

> +					struct rdtgroup *rdtgrp, struct mon_evt *mevt)
> +{
> +	int ret = 0;
> +
> +	if (!assign || strlen(assign) != 1)
> +		return -EINVAL;
> +
> +	switch (*assign) {
> +	case 'e':
> +		ret = rdtgroup_assign_cntr_event(d, rdtgrp, mevt);

This patch enables the user to assign counters to multiple events in a
single write. Looking at this flow:
rdtgroup_assign_cntr_event()->rdtgroup_alloc_config_cntr() may thus
be called on the same domain but for different events in a single write from
user space.
I thus think that the error message in rdtgroup_alloc_config_cntr()
should not just contain the domain ID, but also the event *name*
(not the ID since user space cannot be expect to understand if).
considering this it seems that @mevt can be passed through
to rdtgroup_alloc_config_cntr() instead of just the event ID to support
this?

> +		break;
> +	case '_':
> +		rdtgroup_unassign_cntr_event(d, rdtgrp, mevt);
> +		break;
> +	default:
> +		ret = -EINVAL;

Please add a "break".

> +	}
> +
> +	return ret;
> +}
> +
> +static int resctrl_process_assign(struct rdt_resource *r, struct rdtgroup *rdtgrp,

Please move to monitor.c and rename to be more specific. For example, 
resctrl_parse_mbm_assignment()? Open to ideas.

> +				  char *event, char *tok)
> +{
> +	struct rdt_mon_domain *d;
> +	unsigned long dom_id = 0;
> +	char *dom_str, *id_str;
> +	struct mon_evt *mevt;
> +	int ret;
> +
> +	mevt = mbm_get_mon_event_by_name(r, event);
> +	if (!mevt) {
> +		rdt_last_cmd_printf("Invalid event %s\n", event);
> +		return  -ENOENT;
> +	}
> +
> +next:
> +	if (!tok || tok[0] == '\0')
> +		return 0;
> +
> +	/* Start processing the strings for each domain */
> +	dom_str = strim(strsep(&tok, ";"));
> +
> +	id_str = strsep(&dom_str, "=");
> +
> +	/* Check for domain id '*' which means all domains */
> +	if (id_str && *id_str == '*') {
> +		ret = rdtgroup_modify_assign_state(dom_str, NULL, rdtgrp, mevt);
> +		if (ret)
> +			rdt_last_cmd_printf("Assign operation '%s:*=%s' failed\n",
> +					    event, dom_str);
> +		return ret;
> +	} else if (!id_str || kstrtoul(id_str, 10, &dom_id)) {
> +		rdt_last_cmd_puts("Missing domain id\n");
> +		return -EINVAL;
> +	}
> +
> +	/* Verify if the dom_id is valid */
> +	list_for_each_entry(d, &r->mon_domains, hdr.list) {
> +		if (d->hdr.id == dom_id) {
> +			ret = rdtgroup_modify_assign_state(dom_str, d, rdtgrp, mevt);
> +			if (ret) {
> +				rdt_last_cmd_printf("Assign operation '%s:%ld=%s' failed\n",
> +						    event, dom_id, dom_str);
> +				return ret;
> +			}
> +			goto next;
> +		}
> +	}
> +
> +	rdt_last_cmd_printf("Invalid domain id %ld\n", dom_id);
> +	return -EINVAL;
> +}
> +
Reinette

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