Re: [PATCH V4 6/7] arm64/perf: Add BRBE driver

On 11/2/22 21:06, James Clark wrote:

On 17/10/2022 06:57, Anshuman Khandual wrote:

quoted

This adds a BRBE driver which implements all the required helper functions
for struct arm_pmu. Following functions are defined by this driver which
will configure, enable, capture, reset and disable BRBE buffer HW as and
when requested via perf branch stack sampling framework.

- arm64_pmu_brbe_filter()
- arm64_pmu_brbe_enable()
- arm64_pmu_brbe_disable()
- arm64_pmu_brbe_read()
- arm64_pmu_brbe_probe()
- arm64_pmu_brbe_reset()
- arm64_pmu_brbe_supported()

Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Arnaldo Carvalho de Melo <acme@kernel.org>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Will Deacon <will@kernel.org>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: linux-arm-kernel@lists.infradead.org
Cc: linux-perf-users@vger.kernel.org
Cc: linux-kernel@vger.kernel.org
Signed-off-by: Anshuman Khandual <redacted>
---
 arch/arm64/kernel/perf_event.c |   8 +-
 drivers/perf/Kconfig           |  11 +
 drivers/perf/Makefile          |   1 +
 drivers/perf/arm_pmu_brbe.c    | 441 +++++++++++++++++++++++++++++++++
 drivers/perf/arm_pmu_brbe.h    | 259 +++++++++++++++++++
 include/linux/perf/arm_pmu.h   |  20 ++
 6 files changed, 739 insertions(+), 1 deletion(-)
 create mode 100644 drivers/perf/arm_pmu_brbe.c
 create mode 100644 drivers/perf/arm_pmu_brbe.h

diff --git a/arch/arm64/kernel/perf_event.c b/arch/arm64/kernel/perf_event.c
index 97db333d1208..85a3aaefc0fb 100644
--- a/arch/arm64/kernel/perf_event.c
+++ b/arch/arm64/kernel/perf_event.c

@@ -1034,31 +1034,37 @@ static int armv8pmu_filter_match(struct perf_event *event)
 
 static void armv8pmu_brbe_filter(struct pmu_hw_events *hw_event, struct perf_event *event)
 {
+	arm64_pmu_brbe_filter(hw_event, event);
 }
 
 static void armv8pmu_brbe_enable(struct pmu_hw_events *hw_event)
 {
+	arm64_pmu_brbe_enable(hw_event);
 }
 
 static void armv8pmu_brbe_disable(struct pmu_hw_events *hw_event)
 {
+	arm64_pmu_brbe_disable(hw_event);
 }
 
 static void armv8pmu_brbe_read(struct pmu_hw_events *hw_event, struct perf_event *event)
 {
+	arm64_pmu_brbe_read(hw_event, event);
 }
 
 static void armv8pmu_brbe_probe(struct pmu_hw_events *hw_event)
 {
+	arm64_pmu_brbe_probe(hw_event);
 }
 
 static void armv8pmu_brbe_reset(struct pmu_hw_events *hw_event)
 {
+	arm64_pmu_brbe_reset(hw_event);
 }
 
 static bool armv8pmu_brbe_supported(struct perf_event *event)
 {
-	return false;
+	return arm64_pmu_brbe_supported(event);
 }
 
 static void armv8pmu_reset(void *info)

diff --git a/drivers/perf/Kconfig b/drivers/perf/Kconfig
index 341010f20b77..4efd0a77c5ff 100644
--- a/drivers/perf/Kconfig
+++ b/drivers/perf/Kconfig

@@ -190,6 +190,17 @@ config ALIBABA_UNCORE_DRW_PMU
 	  Support for Driveway PMU events monitoring on Yitian 710 DDR
 	  Sub-system.
 
+config ARM_BRBE_PMU
+	tristate "Enable support for Branch Record Buffer Extension (BRBE)"

Hi Anshuman,

I get a few build errors if this is enabled as a module, and it's
missing the module boilerplate stuff. I'm wondering if tristate is a
mistake and it's supposed to be static only? Otherwise it probably needs
a few different things fixing up.

It would be nice to have it as a module so it's easy to work on in the
future.

quoted

+	depends on ARM64 && ARM_PMU
+	default y

Should this be default m?

Right, "Tristate" here does not really make sense as ARM_BRBE_PMU is dependent
on base ARM_PMU, where as ARM_SPE is abstracted as a separate PMU in itself.

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