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SubjectRe: [PATCH V5 2/8] perf: Extend branch type classification
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On 04/04/2022 05:50, Anshuman Khandual wrote:
> branch_entry.type now has ran out of space to accommodate more branch types
> classification. This will prevent perf branch stack implementation on arm64
> (via BRBE) to capture all available branch types. Extending this bit field
> i.e branch_entry.type [4 bits] is not an option as it will break user space
> ABI both for little and big endian perf tools.
>
> Extend branch classification with a new field branch_entry.new_type via a
> new branch type PERF_BR_EXTEND_ABI in branch_entry.type. Perf tools which
> could decode PERF_BR_EXTEND_ABI, will then parse branch_entry.new_type as
> well.
>
> branch_entry.new_type is a 4 bit field which can hold upto 16 branch types.
> The first three branch types will hold various generic page faults followed
> by five architecture specific branch types, which can be overridden by the
> platform for specific use cases. These architecture specific branch types
> gets overridden on arm64 platform for BRBE implementation.
>
> New generic branch types
>
> - PERF_BR_NEW_FAULT_ALGN
> - PERF_BR_NEW_FAULT_DATA
> - PERF_BR_NEW_FAULT_INST
>
> New arch specific branch types
>
> - PERF_BR_NEW_ARCH_1
> - PERF_BR_NEW_ARCH_2
> - PERF_BR_NEW_ARCH_3
> - PERF_BR_NEW_ARCH_4
> - PERF_BR_NEW_ARCH_5
>
> 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: Alexander Shishkin <alexander.shishkin@linux.intel.com>
> Cc: Jiri Olsa <jolsa@redhat.com>
> Cc: Namhyung Kim <namhyung@kernel.org>
> Cc: Thomas Gleixner <tglx@linutronix.de>
> Cc: Will Deacon <will@kernel.org>
> 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>

Reviewed-by: James Clark <james.clark@arm.com>

> ---
> include/uapi/linux/perf_event.h | 16 +++++++++++++++-
> 1 file changed, 15 insertions(+), 1 deletion(-)
>
> diff --git a/include/uapi/linux/perf_event.h b/include/uapi/linux/perf_event.h
> index 26d8f0b5ac0d..d29280adc3c4 100644
> --- a/include/uapi/linux/perf_event.h
> +++ b/include/uapi/linux/perf_event.h
> @@ -255,9 +255,22 @@ enum {
> PERF_BR_IRQ = 12, /* irq */
> PERF_BR_SERROR = 13, /* system error */
> PERF_BR_NO_TX = 14, /* not in transaction */
> + PERF_BR_EXTEND_ABI = 15, /* extend ABI */
> PERF_BR_MAX,
> };
>
> +enum {
> + PERF_BR_NEW_FAULT_ALGN = 0, /* Alignment fault */
> + PERF_BR_NEW_FAULT_DATA = 1, /* Data fault */
> + PERF_BR_NEW_FAULT_INST = 2, /* Inst fault */
> + PERF_BR_NEW_ARCH_1 = 3, /* Architecture specific */
> + PERF_BR_NEW_ARCH_2 = 4, /* Architecture specific */
> + PERF_BR_NEW_ARCH_3 = 5, /* Architecture specific */
> + PERF_BR_NEW_ARCH_4 = 6, /* Architecture specific */
> + PERF_BR_NEW_ARCH_5 = 7, /* Architecture specific */
> + PERF_BR_NEW_MAX,
> +};
> +
> #define PERF_SAMPLE_BRANCH_PLM_ALL \
> (PERF_SAMPLE_BRANCH_USER|\
> PERF_SAMPLE_BRANCH_KERNEL|\
> @@ -1372,7 +1385,8 @@ struct perf_branch_entry {
> abort:1, /* transaction abort */
> cycles:16, /* cycle count to last branch */
> type:4, /* branch type */
> - reserved:40;
> + new_type:4, /* additional branch type */
> + reserved:36;
> };
>
> union perf_sample_weight {

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