[PATCH v9 7/9] x86/resctrl: Add write option to "mba_MBps_event" file

Tony Luck
2024-11-14T00:17:23Z

The "mba_MBps" mount option provides an alternate method to control memory
bandwidth. Instead of specifying allowable bandwidth as a percentage of
maximum possible, the user provides a MiB/s limit value.

Historically the limit was enforced by a feedback loop from the measure
local bandwidth to adjust the memory bandwidth allocation controls.

There is a file in each ctrl_mon group directory that shows the event
currently in use (always says "mbm_local_bytes").

Allow writing that file to choose a different event.

A user can choose any of the memory bandwidth monitoring events listed in
/sys/fs/resctrl/info/L3_mon/mon_features independently for each ctrl_mon
group by writing to the "mba_MBps_event" file.

Signed-off-by: Tony Luck <tony.luck@intel.com>
---
arch/x86/kernel/cpu/resctrl/internal.h | 2 ++
arch/x86/kernel/cpu/resctrl/ctrlmondata.c | 40 +++++++++++++++++++++++
arch/x86/kernel/cpu/resctrl/rdtgroup.c | 3 +-
3 files changed, 44 insertions(+), 1 deletion(-)

diff --git a/arch/x86/kernel/cpu/resctrl/internal.h b/arch/x86/kernel/cpu/resctrl/internal.h
index ce10a883ecf8..6345ab3e0890 100644
--- a/arch/x86/kernel/cpu/resctrl/internal.h
+++ b/arch/x86/kernel/cpu/resctrl/internal.h
@@ -609,6 +609,8 @@ ssize_t rdtgroup_schemata_write(struct kernfs_open_file *of,
char *buf, size_t nbytes, loff_t off);
int rdtgroup_schemata_show(struct kernfs_open_file *of,
struct seq_file *s, void *v);
+ssize_t rdtgroup_mba_mbps_event_write(struct kernfs_open_file *of,
+ char *buf, size_t nbytes, loff_t off);
int rdtgroup_mba_mbps_event_show(struct kernfs_open_file *of,
struct seq_file *s, void *v);
bool rdtgroup_cbm_overlaps(struct resctrl_schema *s, struct rdt_ctrl_domain *d,
diff --git a/arch/x86/kernel/cpu/resctrl/ctrlmondata.c b/arch/x86/kernel/cpu/resctrl/ctrlmondata.c
index 5fa37b4ecc7a..ee983b68c046 100644
--- a/arch/x86/kernel/cpu/resctrl/ctrlmondata.c
+++ b/arch/x86/kernel/cpu/resctrl/ctrlmondata.c
@@ -518,6 +518,46 @@ static int smp_mon_event_count(void *arg)
return 0;
}

+ssize_t rdtgroup_mba_mbps_event_write(struct kernfs_open_file *of,
+ char *buf, size_t nbytes, loff_t off)
+{
+ struct rdtgroup *rdtgrp;
+ int ret = 0;
+
+ /* Valid input requires a trailing newline */
+ if (nbytes == 0 || buf[nbytes - 1] != '\n')
+ return -EINVAL;
+ buf[nbytes - 1] = '\0';
+
+ rdtgrp = rdtgroup_kn_lock_live(of->kn);
+ if (!rdtgrp) {
+ rdtgroup_kn_unlock(of->kn);
+ return -ENOENT;
+ }
+ rdt_last_cmd_clear();
+
+ if (!strcmp(buf, "mbm_local_bytes")) {
+ if (is_mbm_local_enabled())
+ rdtgrp->mba_mbps_event = QOS_L3_MBM_LOCAL_EVENT_ID;
+ else
+ ret = -EINVAL;
+ } else if (!strcmp(buf, "mbm_total_bytes")) {
+ if (is_mbm_total_enabled())
+ rdtgrp->mba_mbps_event = QOS_L3_MBM_TOTAL_EVENT_ID;
+ else
+ ret = -EINVAL;
+ } else {
+ ret = -EINVAL;
+ }
+
+ if (ret)
+ rdt_last_cmd_printf("Unsupported event id '%s'\n", buf);
+
+ rdtgroup_kn_unlock(of->kn);
+
+ return ret ?: nbytes;
+}
+
int rdtgroup_mba_mbps_event_show(struct kernfs_open_file *of,
struct seq_file *s, void *v)
{
diff --git a/arch/x86/kernel/cpu/resctrl/rdtgroup.c b/arch/x86/kernel/cpu/resctrl/rdtgroup.c
index 416e1acfad9f..3f2e035208e6 100644
--- a/arch/x86/kernel/cpu/resctrl/rdtgroup.c
+++ b/arch/x86/kernel/cpu/resctrl/rdtgroup.c
@@ -1945,8 +1945,9 @@ static struct rftype res_common_files[] = {
},
{
.name = "mba_MBps_event",
- .mode = 0444,
+ .mode = 0644,
.kf_ops = &rdtgroup_kf_single_ops,
+ .write = rdtgroup_mba_mbps_event_write,
.seq_show = rdtgroup_mba_mbps_event_show,
},
{
--
2.47.0