Re: [PATCH V7 0/6] arm64/perf: Enable branch stack sampling

James Clark
2023-01-06T10:24:34Z

On 05/01/2023 03:10, Anshuman Khandual wrote:
> This series enables perf branch stack sampling support on arm64 platform
> via a new arch feature called Branch Record Buffer Extension (BRBE). All
> relevant register definitions could be accessed here.
>

Hi Anshuman,

The missing cc for linux-perf-users@vger.kernel.org on the other patches
means that this looks incomplete on the lore page for linux-perf-users.
b4 still picks up the full set, so it's probably fine. But it might be
worth adding the same cc for all patches next time.

Thanks
James

> https://developer.arm.com/documentation/ddi0601/2021-12/AArch64-Registers
>
> This series applies on v6.2-r2.
>
> Changes in V7:
>
> - Folded [PATCH 7/7] into [PATCH 3/7] which enables branch stack sampling event
> - Defined BRBFCR_EL1_BRANCH_FILTERS, BRBCR_EL1_DEFAULT_CONFIG in the header
> - Defined BRBFCR_EL1_DEFAULT_CONFIG in the header
> - Updated BRBCR_EL1_DEFAULT_CONFIG with BRBCR_EL1_FZP
> - Defined BRBCR_EL1_DEFAULT_TS in the header
> - Updated BRBCR_EL1_DEFAULT_CONFIG with BRBCR_EL1_DEFAULT_TS
> - Moved BRBCR_EL1_DEFAULT_CONFIG check inside branch_type_to_brbcr()
> - Moved down BRBCR_EL1_CC, BRBCR_EL1_MPRED later in branch_type_to_brbcr()
> - Also set BRBE in paused state in armv8pmu_branch_disable()
> - Dropped brbe_paused(), set_brbe_paused() helpers
> - Extracted error string via branch_filter_error_msg[] for armv8pmu_branch_valid()
> - Replaced brbe_v1p1 with brbe_version in struct brbe_hw_attr
> - Added valid_brbe_[cc, format, version]() helpers
> - Split a separate brbe_attributes_probe() from armv8pmu_branch_probe()
> - Capture event->attr.branch_sample_type earlier in armv8pmu_branch_valid()
> - Defined enum brbe_bank_idx with possible values for BRBE bank indices
> - Changed armpmu->hw_attr into armpmu->private
> - Added missing space in stub definition for armv8pmu_branch_valid()
> - Replaced both kmalloc() with kzalloc()
> - Added BRBE_BANK_MAX_ENTRIES
> - Updated comment for capture_brbe_flags()
> - Updated comment for struct brbe_hw_attr
> - Dropped space after type cast in couple of places
> - Replaced inverse with negation for testing BRBCR_EL1_FZP in armv8pmu_branch_read()
> - Captured cpuc->branches->branch_entries[idx] in a local variable
> - Dropped saved_priv from armv8pmu_branch_read()
> - Reorganize PERF_SAMPLE_BRANCH_NO_[CYCLES|NO_FLAGS] related configuration
> - Replaced with FIELD_GET() and FIELD_PREP() wherever applicable
> - Replaced BRBCR_EL1_TS_PHYSICAL with BRBCR_EL1_TS_VIRTUAL
> - Moved valid_brbe_nr(), valid_brbe_cc(), valid_brbe_format(), valid_brbe_version()
> select_brbe_bank(), select_brbe_bank_index() helpers inside the C implementation
> - Reorganized brbe_valid_nr() and dropped the pr_warn() message
> - Changed probe sequence in brbe_attributes_probe()
> - Added 'brbcr' argument into capture_brbe_flags() to ascertain correct state
> - Disable BRBE before disabling the PMU event counter
> - Enable PERF_SAMPLE_BRANCH_HV filters when is_kernel_in_hyp_mode()
> - Guard armv8pmu_reset() & armv8pmu_sched_task() with arm_pmu_branch_stack_supported()
>
> Changes in V6:
>
> https://lore.kernel.org/linux-arm-kernel/20221208084402.863310-1-anshuman.khandual@arm.com/
>
> - Restore the exception level privilege after reading the branch records
> - Unpause the buffer after reading the branch records
> - Decouple BRBCR_EL1_EXCEPTION/ERTN from perf event privilege level
> - Reworked BRBE implementation and branch stack sampling support on arm pmu
> - BRBE implementation is now part of overall ARMV8 PMU implementation
> - BRBE implementation moved from drivers/perf/ to inside arch/arm64/kernel/
> - CONFIG_ARM_BRBE_PMU renamed as CONFIG_ARM64_BRBE in arch/arm64/Kconfig
> - File moved - drivers/perf/arm_pmu_brbe.c -> arch/arm64/kernel/brbe.c
> - File moved - drivers/perf/arm_pmu_brbe.h -> arch/arm64/kernel/brbe.h
> - BRBE name has been dropped from struct arm_pmu and struct hw_pmu_events
> - BRBE name has been abstracted out as 'branches' in arm_pmu and hw_pmu_events
> - BRBE name has been abstracted out as 'branches' in ARMV8 PMU implementation
> - Added sched_task() callback into struct arm_pmu
> - Added 'hw_attr' into struct arm_pmu encapsulating possible PMU HW attributes
> - Dropped explicit attributes brbe_(v1p1, nr, cc, format) from struct arm_pmu
> - Dropped brbfcr, brbcr, registers scratch area from struct hw_pmu_events
> - Dropped brbe_users, brbe_context tracking in struct hw_pmu_events
> - Added 'features' tracking into struct arm_pmu with ARM_PMU_BRANCH_STACK flag
> - armpmu->hw_attr maps into 'struct brbe_hw_attr' inside BRBE implementation
> - Set ARM_PMU_BRANCH_STACK in 'arm_pmu->features' after successful BRBE probe
> - Added armv8pmu_branch_reset() inside armv8pmu_branch_enable()
> - Dropped brbe_supported() as events will be rejected via ARM_PMU_BRANCH_STACK
> - Dropped set_brbe_disabled() as well
> - Reformated armv8pmu_branch_valid() warnings while rejecting unsupported events
>
> Changes in V5:
>
> https://lore.kernel.org/linux-arm-kernel/20221107062514.2851047-1-anshuman.khandual@arm.com/
>
> - Changed BRBCR_EL1.VIRTUAL from 0b1 to 0b01
> - Changed BRBFCR_EL1.EnL into BRBFCR_EL1.EnI
> - Changed config ARM_BRBE_PMU from 'tristate' to 'bool'
>
> Changes in V4:
>
> https://lore.kernel.org/all/20221017055713.451092-1-anshuman.khandual@arm.com/
>
> - Changed ../tools/sysreg declarations as suggested
> - Set PERF_SAMPLE_BRANCH_STACK in data.sample_flags
> - Dropped perfmon_capable() check in armpmu_event_init()
> - s/pr_warn_once/pr_info in armpmu_event_init()
> - Added brbe_format element into struct pmu_hw_events
> - Changed v1p1 as brbe_v1p1 in struct pmu_hw_events
> - Dropped pr_info() from arm64_pmu_brbe_probe(), solved LOCKDEP warning
>
> Changes in V3:
>
> https://lore.kernel.org/all/20220929075857.158358-1-anshuman.khandual@arm.com/
>
> - Moved brbe_stack from the stack and now dynamically allocated
> - Return PERF_BR_PRIV_UNKNOWN instead of -1 in brbe_fetch_perf_priv()
> - Moved BRBIDR0, BRBCR, BRBFCR registers and fields into tools/sysreg
> - Created dummy BRBINF_EL1 field definitions in tools/sysreg
> - Dropped ARMPMU_EVT_PRIV framework which cached perfmon_capable()
> - Both exception and exception return branche records are now captured
> only if the event has PERF_SAMPLE_BRANCH_KERNEL which would already
> been checked in generic perf via perf_allow_kernel()
>
> Changes in V2:
>
> https://lore.kernel.org/all/20220908051046.465307-1-anshuman.khandual@arm.com/
>
> - Dropped branch sample filter helpers consolidation patch from this series
> - Added new hw_perf_event.flags element ARMPMU_EVT_PRIV to cache perfmon_capable()
> - Use cached perfmon_capable() while configuring BRBE branch record filters
>
> Changes in V1:
>
> https://lore.kernel.org/linux-arm-kernel/20220613100119.684673-1-anshuman.khandual@arm.com/
>
> - Added CONFIG_PERF_EVENTS wrapper for all branch sample filter helpers
> - Process new perf branch types via PERF_BR_EXTEND_ABI
>
> Changes in RFC V2:
>
> https://lore.kernel.org/linux-arm-kernel/20220412115455.293119-1-anshuman.khandual@arm.com/
>
> - Added branch_sample_priv() while consolidating other branch sample filter helpers
> - Changed all SYS_BRBXXXN_EL1 register definition encodings per Marc
> - Changed the BRBE driver as per proposed BRBE related perf ABI changes (V5)
> - Added documentation for struct arm_pmu changes, updated commit message
> - Updated commit message for BRBE detection infrastructure patch
> - PERF_SAMPLE_BRANCH_KERNEL gets checked during arm event init (outside the driver)
> - Branch privilege state capture mechanism has now moved inside the driver
>
> Changes in RFC V1:
>
> https://lore.kernel.org/all/1642998653-21377-1-git-send-email-anshuman.khandual@arm.com/
>
> Cc: Catalin Marinas <catalin.marinas@arm.com>
> Cc: Will Deacon <will@kernel.org>
> Cc: Mark Rutland <mark.rutland@arm.com>
> Cc: Mark Brown <broonie@kernel.org>
> Cc: James Clark <james.clark@arm.com>
> Cc: Rob Herring <robh@kernel.org>
> Cc: Marc Zyngier <maz@kernel.org>
> Cc: Suzuki Poulose <suzuki.poulose@arm.com>
> Cc: Peter Zijlstra <peterz@infradead.org>
> Cc: Ingo Molnar <mingo@redhat.com>
> Cc: Arnaldo Carvalho de Melo <acme@kernel.org>
> Cc: linux-arm-kernel@lists.infradead.org
> Cc: linux-perf-users@vger.kernel.org
> Cc: linux-kernel@vger.kernel.org
>
> Anshuman Khandual (6):
> drivers: perf: arm_pmu: Add new sched_task() callback
> arm64/perf: Add BRBE registers and fields
> arm64/perf: Add branch stack support in struct arm_pmu
> arm64/perf: Add branch stack support in struct pmu_hw_events
> arm64/perf: Add branch stack support in ARMV8 PMU
> arm64/perf: Enable branch stack events via FEAT_BRBE
>
> arch/arm64/Kconfig | 11 +
> arch/arm64/include/asm/perf_event.h | 19 ++
> arch/arm64/include/asm/sysreg.h | 103 ++++++
> arch/arm64/kernel/Makefile | 1 +
> arch/arm64/kernel/brbe.c | 512 ++++++++++++++++++++++++++++
> arch/arm64/kernel/brbe.h | 257 ++++++++++++++
> arch/arm64/kernel/perf_event.c | 35 ++
> arch/arm64/tools/sysreg | 161 +++++++++
> drivers/perf/arm_pmu.c | 12 +-
> include/linux/perf/arm_pmu.h | 19 ++
> 10 files changed, 1128 insertions(+), 2 deletions(-)
> create mode 100644 arch/arm64/kernel/brbe.c
> create mode 100644 arch/arm64/kernel/brbe.h