Re: [PATCH V2 6/7] arm64/perf: Add BRBE driver

Anshuman Khandual
2022-09-13T11:38:42Z

On 9/13/22 16:09, James Clark wrote:
>
>
> On 08/09/2022 06:10, Anshuman Khandual wrote:
>> 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 <anshuman.khandual@arm.com>
>> ---
>> arch/arm64/kernel/perf_event.c | 8 +-
>> drivers/perf/Kconfig | 11 +
>> drivers/perf/Makefile | 1 +
>> drivers/perf/arm_pmu_brbe.c | 448 +++++++++++++++++++++++++++++++++
>> drivers/perf/arm_pmu_brbe.h | 259 +++++++++++++++++++
>> include/linux/perf/arm_pmu.h | 20 ++
>> 6 files changed, 746 insertions(+), 1 deletion(-)
>> create mode 100644 drivers/perf/arm_pmu_brbe.c
>> create mode 100644 drivers/perf/arm_pmu_brbe.h
>>
> [...]
>> +
>> +static int brbe_fetch_perf_priv(u64 brbinf)
>> +{
>> + int brbe_el = brbe_fetch_el(brbinf);
>> +
>> + switch (brbe_el) {
>> + case BRBINF_EL_EL0:
>> + return PERF_BR_PRIV_USER;
>> + case BRBINF_EL_EL1:
>> + return PERF_BR_PRIV_KERNEL;
>> + case BRBINF_EL_EL2:
>> + if (is_kernel_in_hyp_mode())
>> + return PERF_BR_PRIV_KERNEL;
>> + return PERF_BR_PRIV_HV;
>> + default:
>> + pr_warn("unknown branch privilege captured\n");
>> + return -1;
>
> On V1 you said that you would change this to PERF_BR_PRIV_UNKNOWN, looks
> like that was dropped. Unless it didn't work out?

Seems like it just got dropped unintentionally. Yes, PERF_BR_PRIV_UNKNOWN
can be returned here instead of "-1", similar to brbe_fetch_perf_type()
which returns PERF_BR_UNKNOWN.