[PATCH v13 24/32] x86/resctrl: Add energy/perf choices to rdt boot option

Tony Luck
2025-10-29T16:21:44Z

Legacy resctrl features are enumerated by X86_FEATURE_* flags. These
may be overridden by quirks to disable features in the case of errata.
Users can use kernel command line options to either disable a feature,
or to force enable a feature that was disabled by a quirk.

Provide similar functionality for hardware features that do not have an
X86_FEATURE_* flag. Unlike other features that are tied to X86_FEATURE_*
flags, these must be queried by name. Add rdt_is_feature_enabled()
to check whether quirks or kernel command line have disabled a feature.

Users may force a feature to be disabled. E.g. "rdt=!perf" will ensure
that none of the perf telemetry events are enabled.

Resctrl architecture code may disable a feature that does not provide
full functionality. Users may override that decision. E.g. "rdt=energy"
will enable any available energy telemetry events even if they do not
provide full functionality.

Signed-off-by: Tony Luck <tony.luck@intel.com>
Reviewed-by: Reinette Chatre <reinette.chatre@intel.com>
---
.../admin-guide/kernel-parameters.txt | 2 +-
arch/x86/kernel/cpu/resctrl/internal.h | 2 ++
arch/x86/kernel/cpu/resctrl/core.c | 29 +++++++++++++++++++
3 files changed, 32 insertions(+), 1 deletion(-)

diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
index 6c42061ca20e..bb8f5d73ebf8 100644
--- a/Documentation/admin-guide/kernel-parameters.txt
+++ b/Documentation/admin-guide/kernel-parameters.txt
@@ -6207,7 +6207,7 @@
rdt= [HW,X86,RDT]
Turn on/off individual RDT features. List is:
cmt, mbmtotal, mbmlocal, l3cat, l3cdp, l2cat, l2cdp,
- mba, smba, bmec, abmc.
+ mba, smba, bmec, abmc, energy, perf.
E.g. to turn on cmt and turn off mba use:
rdt=cmt,!mba

diff --git a/arch/x86/kernel/cpu/resctrl/internal.h b/arch/x86/kernel/cpu/resctrl/internal.h
index b920f54f8736..e3710b9f993e 100644
--- a/arch/x86/kernel/cpu/resctrl/internal.h
+++ b/arch/x86/kernel/cpu/resctrl/internal.h
@@ -225,6 +225,8 @@ void __init intel_rdt_mbm_apply_quirk(void);
void rdt_domain_reconfigure_cdp(struct rdt_resource *r);
void resctrl_arch_mbm_cntr_assign_set_one(struct rdt_resource *r);

+bool rdt_is_feature_enabled(char *name);
+
#ifdef CONFIG_X86_CPU_RESCTRL_INTEL_AET
bool intel_aet_get_events(void);
void __exit intel_aet_exit(void);
diff --git a/arch/x86/kernel/cpu/resctrl/core.c b/arch/x86/kernel/cpu/resctrl/core.c
index ba1ddc2eec15..7013911d3575 100644
--- a/arch/x86/kernel/cpu/resctrl/core.c
+++ b/arch/x86/kernel/cpu/resctrl/core.c
@@ -772,6 +772,8 @@ enum {
RDT_FLAG_SMBA,
RDT_FLAG_BMEC,
RDT_FLAG_ABMC,
+ RDT_FLAG_ENERGY,
+ RDT_FLAG_PERF,
};

#define RDT_OPT(idx, n, f) \
@@ -798,6 +800,8 @@ static struct rdt_options rdt_options[] __ro_after_init = {
RDT_OPT(RDT_FLAG_SMBA, "smba", X86_FEATURE_SMBA),
RDT_OPT(RDT_FLAG_BMEC, "bmec", X86_FEATURE_BMEC),
RDT_OPT(RDT_FLAG_ABMC, "abmc", X86_FEATURE_ABMC),
+ RDT_OPT(RDT_FLAG_ENERGY, "energy", 0),
+ RDT_OPT(RDT_FLAG_PERF, "perf", 0),
};
#define NUM_RDT_OPTIONS ARRAY_SIZE(rdt_options)

@@ -847,6 +851,31 @@ bool rdt_cpu_has(int flag)
return ret;
}

+/*
+ * Hardware features that do not have X86_FEATURE_* bits. There is no
+ * "hardware does not support this at all" case. Assume that the caller
+ * has already determined that hardware support is present and just needs
+ * to check if the feature has been disabled by a quirk that has not been
+ * overridden by a command line option.
+ */
+bool rdt_is_feature_enabled(char *name)
+{
+ struct rdt_options *o;
+ bool ret = true;
+
+ for (o = rdt_options; o < &rdt_options[NUM_RDT_OPTIONS]; o++) {
+ if (!strcmp(name, o->name)) {
+ if (o->force_off)
+ ret = false;
+ if (o->force_on)
+ ret = true;
+ break;
+ }
+ }
+
+ return ret;
+}
+
bool resctrl_arch_is_evt_configurable(enum resctrl_event_id evt)
{
if (!rdt_cpu_has(X86_FEATURE_BMEC))
--
2.51.0