Message-ID: <7869219493bb4cc5626da704c4f8f107fe7c8f69.1752013061.git.babu.moger@amd.com>
Date: Tue, 8 Jul 2025 17:17:42 -0500
From: Babu Moger <babu.moger@....com>
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Subject: [PATCH v15 33/34] fs/resctrl: Introduce the interface to switch between monitor modes

Resctrl subsystem can support two monitoring modes, "mbm_event" or
"default". In mbm_event mode, 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 mbm_assign_mode resctrl file to switch between mbm_event and
default modes.

Example:
To list the MBM monitor modes supported:
$ cat /sys/fs/resctrl/info/L3_MON/mbm_assign_mode
[mbm_event]
default

To enable the "mbm_event" monitoring mode:
$ echo "mbm_event" > /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. Also clear assignable
counter configuration on all the domains.

Signed-off-by: Babu Moger <babu.moger@....com>
---
v15: Minor changelog update.
     Minir user do resctrl.rst update.
     Fixed stray hunks.

v14: Updated the changelog to reflect the change in monitor mode naming.
     Added the call resctrl_bmec_files_show() to enable/disable files
     related to BMEC.
     Added resctrl_set_mon_evt_cfg() to reset event configuration values
     when mode is changes.

v13: Resolved the conflicts due to FS/ARCH restructure.
     Introduced the new resctrl_init_evt_configuration() to initialize
     the event modes and configuration values.
     Added the call to resctrl_bmec_files_show() hide/show BMEC related
     files.

v12: Fixed the documentation for a consistency.
     Introduced mbm_cntr_free_all() and resctrl_reset_rmid_all() to clear
     counters and non-architectural states when monitor mode is changed.
     https://lore.kernel.org/lkml/b60b4f72-6245-46db-a126-428fb13b6310@intel.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/filesystems/resctrl.rst | 22 +++++++-
 fs/resctrl/internal.h                 |  2 +
 fs/resctrl/monitor.c                  | 27 ++++++++++
 fs/resctrl/rdtgroup.c                 | 72 ++++++++++++++++++++++++++-
 4 files changed, 121 insertions(+), 2 deletions(-)

diff --git a/Documentation/filesystems/resctrl.rst b/Documentation/filesystems/resctrl.rst
index 2b2acb55d8b1..b8a4dbe061ea 100644
--- a/Documentation/filesystems/resctrl.rst
+++ b/Documentation/filesystems/resctrl.rst
@@ -259,7 +259,8 @@ with the following files:
 
 "mbm_assign_mode":
 	The supported counter assignment modes. The enclosed brackets indicate which mode
-	is enabled.
+	is enabled. The MBM events associated with counters may reset when "mbm_assign_mode"
+	is changed.
 	::
 
 	  # cat /sys/fs/resctrl/info/L3_MON/mbm_assign_mode
@@ -279,6 +280,15 @@ with the following files:
 	of counters available is described in the "num_mbm_cntrs" file. Changing the
 	mode may cause all counters on the resource to reset.
 
+	Moving to mbm_event counter assignment mode requires 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
@@ -288,6 +298,16 @@ with the following files:
 	result in misleading values or display "Unavailable" if no counter is assigned
 	to the event.
 
+	* To enable "mbm_event" monitoring mode:
+	  ::
+
+	    # echo "mbm_event" > /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 maximum number of counters (total of available and assigned counters) in
 	each domain when the system supports mbm_event mode.
diff --git a/fs/resctrl/internal.h b/fs/resctrl/internal.h
index 9881674909f2..6eb8cce03a65 100644
--- a/fs/resctrl/internal.h
+++ b/fs/resctrl/internal.h
@@ -412,6 +412,8 @@ void rdtgroup_unassign_cntr_event(struct rdt_mon_domain *d, struct rdtgroup *rdt
 int mbm_cntr_get(struct rdt_resource *r, struct rdt_mon_domain *d,
 		 struct rdtgroup *rdtgrp, enum resctrl_event_id evtid);
 void resctrl_update_cntr_allrdtgrp(struct mon_evt *mevt);
+void resctrl_reset_rmid_all(struct rdt_resource *r, struct rdt_mon_domain *d);
+void mbm_cntr_free_all(struct rdt_resource *r, struct rdt_mon_domain *d);
 
 #ifdef CONFIG_RESCTRL_FS_PSEUDO_LOCK
 int rdtgroup_locksetup_enter(struct rdtgroup *rdtgrp);
diff --git a/fs/resctrl/monitor.c b/fs/resctrl/monitor.c
index 61419849b257..f3d9b2ba8360 100644
--- a/fs/resctrl/monitor.c
+++ b/fs/resctrl/monitor.c
@@ -1076,6 +1076,33 @@ static void mbm_cntr_free(struct rdt_mon_domain *d, int cntr_id)
 	memset(&d->cntr_cfg[cntr_id], 0, sizeof(*d->cntr_cfg));
 }
 
+/*
+ * mbm_cntr_free_all() - Clear all the counter ID configuration details in the
+ *			 domain @d. Called when mbm_assign_mode is changed.
+ */
+void mbm_cntr_free_all(struct rdt_resource *r, struct rdt_mon_domain *d)
+{
+	memset(d->cntr_cfg, 0, sizeof(*d->cntr_cfg) * r->mon.num_mbm_cntrs);
+}
+
+/*
+ * resctrl_reset_rmid_all() - Reset all non-architecture states for all the
+ *			      supported RMIDs.
+ */
+void resctrl_reset_rmid_all(struct rdt_resource *r, struct rdt_mon_domain *d)
+{
+	u32 idx_limit = resctrl_arch_system_num_rmid_idx();
+	enum resctrl_event_id evt;
+	int idx;
+
+	for_each_mbm_event_id(evt) {
+		if (!resctrl_is_mon_event_enabled(evt))
+			continue;
+		idx = MBM_STATE_IDX(evt);
+		memset(d->mbm_states[idx], 0, sizeof(*d->mbm_states[0]) * idx_limit);
+	}
+}
+
 /*
  * rdtgroup_alloc_config_cntr() - Allocate a counter ID and configure it for the
  * event pointed to by @mevt and the resctrl group @rdtgrp within the domain @d.
diff --git a/fs/resctrl/rdtgroup.c b/fs/resctrl/rdtgroup.c
index d73057b96d1d..8a7fa1078d02 100644
--- a/fs/resctrl/rdtgroup.c
+++ b/fs/resctrl/rdtgroup.c
@@ -1862,6 +1862,75 @@ static int resctrl_mbm_assign_mode_show(struct kernfs_open_file *of,
 	return 0;
 }
 
+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 = rdt_kn_parent_priv(of->kn);
+	struct rdt_mon_domain *d;
+	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_event")) {
+		if (r->mon.mbm_cntr_assignable) {
+			enable = 1;
+		} else {
+			ret = -EINVAL;
+			rdt_last_cmd_puts("mbm_event mode is not supported\n");
+			goto out_unlock;
+		}
+	} else {
+		ret = -EINVAL;
+		rdt_last_cmd_puts("Unsupported assign mode\n");
+		goto out_unlock;
+	}
+
+	if (enable != resctrl_arch_mbm_cntr_assign_enabled(r)) {
+		ret = resctrl_arch_mbm_cntr_assign_set(r, enable);
+		if (ret)
+			goto out_unlock;
+
+		/* Update the visibility of BMEC related files */
+		resctrl_bmec_files_show(r, !enable);
+
+		/*
+		 * Initialize the default memory transaction values for
+		 * total and local events.
+		 */
+		if (resctrl_is_mon_event_enabled(QOS_L3_MBM_TOTAL_EVENT_ID))
+			mon_event_all[QOS_L3_MBM_TOTAL_EVENT_ID].evt_cfg = MAX_EVT_CONFIG_BITS;
+		if (resctrl_is_mon_event_enabled(QOS_L3_MBM_LOCAL_EVENT_ID))
+			mon_event_all[QOS_L3_MBM_LOCAL_EVENT_ID].evt_cfg = READS_TO_LOCAL_MEM |
+									   READS_TO_LOCAL_S_MEM |
+									   NON_TEMP_WRITE_TO_LOCAL_MEM;
+		/*
+		 * Reset all the non-achitectural RMID state and assignable counters.
+		 */
+		list_for_each_entry(d, &r->mon_domains, hdr.list) {
+			mbm_cntr_free_all(r, d);
+			resctrl_reset_rmid_all(r, d);
+		}
+	}
+
+out_unlock:
+	mutex_unlock(&rdtgroup_mutex);
+	cpus_read_unlock();
+
+	return ret ?: nbytes;
+}
+
 static int resctrl_num_mbm_cntrs_show(struct kernfs_open_file *of,
 				      struct seq_file *s, void *v)
 {
@@ -2369,9 +2438,10 @@ 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 | RFTYPE_RES_CACHE,
 	},
 	{
-- 
2.34.1

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