[PATCH v12 25/26] x86/resctrl: Introduce the interface to switch between monitor modes

Babu Moger
2025-04-04T00:22:42Z

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" monitoring 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>
---
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/arch/x86/resctrl.rst | 25 ++++++++++-
arch/x86/kernel/cpu/resctrl/internal.h | 2 +
arch/x86/kernel/cpu/resctrl/monitor.c | 16 +++++++
arch/x86/kernel/cpu/resctrl/rdtgroup.c | 58 +++++++++++++++++++++++++-
4 files changed, 99 insertions(+), 2 deletions(-)

diff --git a/Documentation/arch/x86/resctrl.rst b/Documentation/arch/x86/resctrl.rst
index ad35c38eed34..05f1852ad8e2 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:
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_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
@@ -284,6 +297,16 @@ with the following files:
misleading values or display "Unavailable" if no counter is assigned
to the event.

+ * To enable "mbm_cntr_assign" monitoring 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 maximum number of monitoring counters (total of available and assigned
counters) in each domain when the system supports mbm_cntr_assign mode.
diff --git a/arch/x86/kernel/cpu/resctrl/internal.h b/arch/x86/kernel/cpu/resctrl/internal.h
index 2020a2fe7135..2f3a5d78d153 100644
--- a/arch/x86/kernel/cpu/resctrl/internal.h
+++ b/arch/x86/kernel/cpu/resctrl/internal.h
@@ -599,6 +599,8 @@ int resctrl_unassign_cntr_event(struct rdt_resource *r, struct rdt_mon_domain *d
struct rdtgroup *rdtgrp, enum resctrl_event_id evtid, u32 evt_cfg);
int mbm_cntr_get(struct rdt_resource *r, struct rdt_mon_domain *d,
struct rdtgroup *rdtgrp, enum resctrl_event_id evtid);
+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/arch/x86/kernel/cpu/resctrl/monitor.c b/arch/x86/kernel/cpu/resctrl/monitor.c
index 0c6fd5f6ec19..7f2e1fdfa936 100644
--- a/arch/x86/kernel/cpu/resctrl/monitor.c
+++ b/arch/x86/kernel/cpu/resctrl/monitor.c
@@ -610,6 +610,17 @@ static struct mbm_state *get_mbm_state(struct rdt_mon_domain *d, u32 closid,
}
}

+void resctrl_reset_rmid_all(struct rdt_resource *r, struct rdt_mon_domain *d)
+{
+ u32 idx_limit = resctrl_arch_system_num_rmid_idx();
+
+ if (resctrl_arch_is_mbm_total_enabled())
+ memset(d->mbm_total, 0, sizeof(struct mbm_state) * idx_limit);
+
+ if (resctrl_arch_is_mbm_local_enabled())
+ memset(d->mbm_local, 0, sizeof(struct mbm_state) * idx_limit);
+}
+
static int __mon_event_count(u32 closid, u32 rmid, struct rmid_read *rr)
{
int cpu = smp_processor_id();
@@ -1558,6 +1569,11 @@ static void mbm_cntr_free(struct rdt_mon_domain *d, int cntr_id)
memset(&d->cntr_cfg[cntr_id], 0, sizeof(struct mbm_cntr_cfg));
}

+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);
+}
+
/*
* Allocate a fresh counter and configure the event if not assigned already.
*/
diff --git a/arch/x86/kernel/cpu/resctrl/rdtgroup.c b/arch/x86/kernel/cpu/resctrl/rdtgroup.c
index 5d9c4c216522..d10cf1e5b914 100644
--- a/arch/x86/kernel/cpu/resctrl/rdtgroup.c
+++ b/arch/x86/kernel/cpu/resctrl/rdtgroup.c
@@ -1050,6 +1050,61 @@ static ssize_t resctrl_mbm_assign_on_mkdir_write(struct kernfs_open_file *of,
return ret ?: nbytes;
}

+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;
+ 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_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)
+ goto write_exit;
+ /*
+ * 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);
+ }
+ }
+
+write_exit:
+ mutex_unlock(&rdtgroup_mutex);
+ cpus_read_unlock();
+
+ return ret ?: nbytes;
+}
+
#ifdef CONFIG_PROC_CPU_RESCTRL

/*
@@ -2412,9 +2467,10 @@ 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