[PATCH v5 07/20] x86/resctrl: Introduce the interface to display monitor mode

Babu Moger
2024-07-03T21:49:43Z

The ABMC feature provides an option to the user to assign a hardware
counter to an RMID and monitor the bandwidth as long as it is assigned.
ABMC mode is enabled by default when supported. System can be one mode
at a time (Legacy monitor mode or ABMC mode).

Provide an interface to display the monitor mode on the system.
$cat /sys/fs/resctrl/info/L3_MON/mbm_mode
[abmc]
legacy

Signed-off-by: Babu Moger <babu.moger@amd.com>
---
v5: Changed interface name to mbm_mode.
It will be always available even if ABMC feature is not supported.
Added description in resctrl.rst about ABMC mode.
Fixed display abmc and legacy consistantly.

v4: Fixed the checks for legacy and abmc mode. Default it ABMC.

v3: New patch to display ABMC capability.
---
Documentation/arch/x86/resctrl.rst | 30 ++++++++++++++++++++++++++
arch/x86/kernel/cpu/resctrl/monitor.c | 2 ++
arch/x86/kernel/cpu/resctrl/rdtgroup.c | 26 ++++++++++++++++++++++
3 files changed, 58 insertions(+)

diff --git a/Documentation/arch/x86/resctrl.rst b/Documentation/arch/x86/resctrl.rst
index 30586728a4cd..108e494fd7cc 100644
--- a/Documentation/arch/x86/resctrl.rst
+++ b/Documentation/arch/x86/resctrl.rst
@@ -257,6 +257,36 @@ with the following files:
# cat /sys/fs/resctrl/info/L3_MON/mbm_local_bytes_config
0=0x30;1=0x30;3=0x15;4=0x15

+"mbm_mode":
+ Reports the list of assignable monitoring features supported. The
+ enclosed brackets indicate which feature is enabled.
+ ::
+
+ cat /sys/fs/resctrl/info/L3_MON/mbm_mode
+ [abmc]
+ legacy
+
+ The bandwidth monitoring feature on AMD system only guarantees that
+ RMIDs currently assigned to a processor will be tracked by hardware.
+ The counters of any other RMIDs which are no longer being tracked
+ will be reset to zero. The MBM event counters return "Unavailable"
+ for the RMIDs that are not tracked by hardware. So, there can be
+ only limited number of groups that can give guaranteed monitoring
+ numbers. With ever changing configurations there is no way to
+ definitely know which of these groups are being tracked for certain
+ point of time. Users do not have the option to monitor a group or
+ set of groups for certain period of time without worrying about
+ RMID being reset in between.
+
+ The ABMC feature provides an option to the user to assign a
+ hardware counter to an RMID and monitor the bandwidth as long as
+ it is assigned. The assigned RMID will be tracked by the hardware
+ until the user unassigns it manually. There is no need to worry
+ about counters being reset during this period.
+
+ Without ABMC enabled, monitoring will work in "legacy" mode
+ without assignment option.
+
"max_threshold_occupancy":
Read/write file provides the largest value (in
bytes) at which a previously used LLC_occupancy
diff --git a/arch/x86/kernel/cpu/resctrl/monitor.c b/arch/x86/kernel/cpu/resctrl/monitor.c
index 12793762ca24..6c4cb36b4b50 100644
--- a/arch/x86/kernel/cpu/resctrl/monitor.c
+++ b/arch/x86/kernel/cpu/resctrl/monitor.c
@@ -1245,6 +1245,8 @@ int __init rdt_get_mon_l3_config(struct rdt_resource *r)
}
}

+ resctrl_file_fflags_init("mbm_mode", RFTYPE_MON_INFO);
+
l3_mon_evt_init(r);

r->mon_capable = true;
diff --git a/arch/x86/kernel/cpu/resctrl/rdtgroup.c b/arch/x86/kernel/cpu/resctrl/rdtgroup.c
index 471fc0dbd7c3..3988d7b86817 100644
--- a/arch/x86/kernel/cpu/resctrl/rdtgroup.c
+++ b/arch/x86/kernel/cpu/resctrl/rdtgroup.c
@@ -845,6 +845,26 @@ static int rdtgroup_rmid_show(struct kernfs_open_file *of,
return ret;
}

+static int rdtgroup_mbm_mode_show(struct kernfs_open_file *of,
+ struct seq_file *s, void *v)
+{
+ struct rdt_resource *r = of->kn->parent->priv;
+
+ if (r->mon.abmc_capable) {
+ if (resctrl_arch_get_abmc_enabled()) {
+ seq_puts(s, "[abmc]\n");
+ seq_puts(s, "legacy\n");
+ } else {
+ seq_puts(s, "abmc\n");
+ seq_puts(s, "[legacy]\n");
+ }
+ } else {
+ seq_puts(s, "[legacy]\n");
+ }
+
+ return 0;
+}
+
#ifdef CONFIG_PROC_CPU_RESCTRL

/*
@@ -1901,6 +1921,12 @@ static struct rftype res_common_files[] = {
.seq_show = mbm_local_bytes_config_show,
.write = mbm_local_bytes_config_write,
},
+ {
+ .name = "mbm_mode",
+ .mode = 0444,
+ .kf_ops = &rdtgroup_kf_single_ops,
+ .seq_show = rdtgroup_mbm_mode_show,
+ },
{
.name = "cpus",
.mode = 0644,
--
2.34.1