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Subject[PATCH V4] arm64: perf: Set PMCR.X of PMCR_EL0 during pmu reset
Date
Enable exporting of events over PMU event export bus by setting
PMCR.X of PMCR_EL0 during pmu reset.

As it impacts power consumption make it configurable at bootup
with kernel arguments and at runtime with sysctl.

Signed-off-by: Srinivasarao Pathipati <quic_c_spathi@quicinc.com>
---
Changes since V3:
- export bit is now configurable with sysctl
- enabling export bit on reset instead of retaining

Changes since V2:
Done below changes as per Will's comments
- enabling pmcr_x now configurable with kernel parameters and
by default it is disabled.

Changes since V1:
- Preserving only PMCR_X bit as per Robin Murphy's comment.
---
Documentation/admin-guide/kernel-parameters.txt | 4 ++++
Documentation/admin-guide/sysctl/kernel.rst | 8 ++++++++
arch/arm64/kernel/perf_event.c | 15 +++++++++++++++
include/linux/perf_event.h | 1 +
kernel/sysctl.c | 12 ++++++++++++
5 files changed, 40 insertions(+)

diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
index de3da15..2139b81 100644
--- a/Documentation/admin-guide/kernel-parameters.txt
+++ b/Documentation/admin-guide/kernel-parameters.txt
@@ -5150,6 +5150,10 @@
Useful for devices that are detected asynchronously
(e.g. USB and MMC devices).

+ export_pmu_events
+ [KNL] Sets export bit of PMCR_EL0 to enable the exporting of
+ events over PMU event export bus.
+
retain_initrd [RAM] Keep initrd memory after extraction

rfkill.default_state=
diff --git a/Documentation/admin-guide/sysctl/kernel.rst b/Documentation/admin-guide/sysctl/kernel.rst
index ddccd10..8fbc3a0 100644
--- a/Documentation/admin-guide/sysctl/kernel.rst
+++ b/Documentation/admin-guide/sysctl/kernel.rst
@@ -892,6 +892,14 @@ The default value is 0 (access disabled).

See Documentation/arm64/perf.rst for more information.

+export_pmu_events
+=================
+Controls the export bit(4th bit) of PMCR_EL0 which enables the exporting of
+events over an IMPLEMENTATION DEFINED PMU event export bus to another device.
+
+0: disables exporting of events
+
+1: enables exporting of events

pid_max
=======
diff --git a/arch/arm64/kernel/perf_event.c b/arch/arm64/kernel/perf_event.c
index cb69ff1..271a8c6 100644
--- a/arch/arm64/kernel/perf_event.c
+++ b/arch/arm64/kernel/perf_event.c
@@ -34,6 +34,7 @@
#define ARMV8_THUNDER_PERFCTR_L1I_CACHE_PREF_ACCESS 0xEC
#define ARMV8_THUNDER_PERFCTR_L1I_CACHE_PREF_MISS 0xED

+int sysctl_export_pmu_events __read_mostly;
/*
* ARMv8 Architectural defined events, not all of these may
* be supported on any given implementation. Unsupported events will
@@ -1025,6 +1026,17 @@ static int armv8pmu_filter_match(struct perf_event *event)
return evtype != ARMV8_PMUV3_PERFCTR_CHAIN;
}

+static int __init export_pmu_events(char *str)
+{
+ /* Exporting of events can be enabled at runtime with sysctl or
+ * statically at bootup with kernel parameters.
+ */
+ sysctl_export_pmu_events = 1;
+ return 0;
+}
+
+early_param("export_pmu_events", export_pmu_events);
+
static void armv8pmu_reset(void *info)
{
struct arm_pmu *cpu_pmu = (struct arm_pmu *)info;
@@ -1047,6 +1059,9 @@ static void armv8pmu_reset(void *info)
if (armv8pmu_has_long_event(cpu_pmu))
pmcr |= ARMV8_PMU_PMCR_LP;

+ if (sysctl_export_pmu_events)
+ pmcr |= ARMV8_PMU_PMCR_X;
+
armv8pmu_pmcr_write(pmcr);
}

diff --git a/include/linux/perf_event.h b/include/linux/perf_event.h
index da75956..7790328 100644
--- a/include/linux/perf_event.h
+++ b/include/linux/perf_event.h
@@ -1311,6 +1311,7 @@ extern void put_callchain_entry(int rctx);

extern int sysctl_perf_event_max_stack;
extern int sysctl_perf_event_max_contexts_per_stack;
+extern int sysctl_export_pmu_events;

static inline int perf_callchain_store_context(struct perf_callchain_entry_ctx *ctx, u64 ip)
{
diff --git a/kernel/sysctl.c b/kernel/sysctl.c
index e52b6e3..3b751a2e 100644
--- a/kernel/sysctl.c
+++ b/kernel/sysctl.c
@@ -2008,6 +2008,18 @@ static struct ctl_table kern_table[] = {
.extra2 = SYSCTL_ONE_THOUSAND,
},
#endif
+#ifdef CONFIG_HW_PERF_EVENTS
+ {
+ .procname = "export_pmu_events",
+ .data = &sysctl_export_pmu_events,
+ .maxlen = sizeof(int),
+ .mode = 0644,
+ .proc_handler = proc_dointvec_minmax,
+ .extra1 = SYSCTL_ZERO,
+ .extra2 = SYSCTL_ONE,
+
+ },
+#endif
{
.procname = "panic_on_warn",
.data = &panic_on_warn,
--
2.7.4
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