[PATCH v3 07/13] perf/x86/amd: make Zen3 branch sampling opt-in

Stephane Eranian
2021-12-01T01:02:58Z

This patch adds a kernel config option to make support
for AMD Zen3 Branch Sampling (BRS) an opt-in compile
time option.

Signed-off-by: Stephane Eranian <eranian@google.com>
---
arch/x86/events/Kconfig | 8 ++++++
arch/x86/events/amd/Makefile | 3 ++-
arch/x86/events/perf_event.h | 49 ++++++++++++++++++++++++++++--------
3 files changed, 49 insertions(+), 11 deletions(-)

diff --git a/arch/x86/events/Kconfig b/arch/x86/events/Kconfig
index d6cdfe631674..1dc002ef66da 100644
--- a/arch/x86/events/Kconfig
+++ b/arch/x86/events/Kconfig
@@ -44,4 +44,12 @@ config PERF_EVENTS_AMD_UNCORE

To compile this driver as a module, choose M here: the
module will be called 'amd-uncore'.
+
+config PERF_EVENTS_AMD_BRS
+ depends on PERF_EVENTS && CPU_SUP_AMD
+ tristate "AMD Zen3 Branch Sampling support"
+ help
+ Enable AMD Zen3 branch sampling support (BRS) which samples up to
+ 16 consecutive taken branches in registers.
+
endmenu
diff --git a/arch/x86/events/amd/Makefile b/arch/x86/events/amd/Makefile
index cf323ffab5cd..b9f5d4610256 100644
--- a/arch/x86/events/amd/Makefile
+++ b/arch/x86/events/amd/Makefile
@@ -1,5 +1,6 @@
# SPDX-License-Identifier: GPL-2.0
-obj-$(CONFIG_CPU_SUP_AMD) += core.o brs.o
+obj-$(CONFIG_CPU_SUP_AMD) += core.o
+obj-$(CONFIG_PERF_EVENTS_AMD_BRS) += brs.o
obj-$(CONFIG_PERF_EVENTS_AMD_POWER) += power.o
obj-$(CONFIG_X86_LOCAL_APIC) += ibs.o
obj-$(CONFIG_PERF_EVENTS_AMD_UNCORE) += amd-uncore.o
diff --git a/arch/x86/events/perf_event.h b/arch/x86/events/perf_event.h
index 74552845d942..a4715bfcb801 100644
--- a/arch/x86/events/perf_event.h
+++ b/arch/x86/events/perf_event.h
@@ -1212,6 +1212,8 @@ static inline bool fixed_counter_disabled(int i, struct pmu *pmu)
#ifdef CONFIG_CPU_SUP_AMD

int amd_pmu_init(void);
+
+#ifdef CONFIG_PERF_EVENTS_AMD_BRS
int amd_brs_init(void);
void amd_brs_disable(void);
void amd_brs_enable(void);
@@ -1246,25 +1248,52 @@ static inline void amd_pmu_brs_del(struct perf_event *event)

void amd_pmu_brs_sched_task(struct perf_event_context *ctx, bool sched_in);

-/*
- * check if BRS is activated on the CPU
- * active defined as it has non-zero users and DBG_EXT_CFG.BRSEN=1
- */
-static inline bool amd_brs_active(void)
+static inline s64 amd_brs_adjust_period(s64 period)
{
- struct cpu_hw_events *cpuc = this_cpu_ptr(&cpu_hw_events);
+ if (period > x86_pmu.lbr_nr)
+ return period - x86_pmu.lbr_nr;

- return cpuc->brs_active;
+ return period;
+}
+#else
+static inline int amd_brs_init(void)
+{
+ return 0;
}
+static inline void amd_brs_disable(void) {}
+static inline void amd_brs_enable(void) {}
+static inline void amd_brs_drain(void) {}
+static inline void amd_brs_lopwr_init(void) {}
+static inline void amd_brs_disable_all(void) {}
+static inline int amd_brs_setup_filter(struct perf_event *event)
+{
+ return 0;
+}
+static inline void amd_brs_reset(void) {}

-static inline s64 amd_brs_adjust_period(s64 period)
+static inline void amd_pmu_brs_add(struct perf_event *event)
{
- if (period > x86_pmu.lbr_nr)
- return period - x86_pmu.lbr_nr;
+}
+
+static inline void amd_pmu_brs_del(struct perf_event *event)
+{
+}
+
+static inline void amd_pmu_brs_sched_task(struct perf_event_context *ctx, bool sched_in)
+{
+}

+static inline s64 amd_brs_adjust_period(s64 period)
+{
return period;
}

+static inline void amd_brs_enable_all(void)
+{
+}
+
+#endif
+
#else /* CONFIG_CPU_SUP_AMD */

static inline int amd_pmu_init(void)
--
2.34.0.rc2.393.gf8c9666880-goog