Re: [RFC V1 10/11] perf: Expand perf_branch_entry.type

[James Clark <james.clark@arm.com>]

On 24/01/2022 04:30, Anshuman Khandual wrote:
> Current perf_branch_entry.type is a 4 bits field just enough to accommodate
> 16 generic branch types. This is insufficient to accommodate platforms like
> arm64 which has much more branch types. Lets just expands this field into a
> 6 bits one, which can now hold 64 generic branch types. This also adds more
> generic branch types and updates the BRBE driver as required.
> 
> 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: 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>
> ---
>  drivers/perf/arm_pmu_brbe.c           |  7 ++++++-
>  include/uapi/linux/perf_event.h       | 10 ++++++++--
>  tools/include/uapi/linux/perf_event.h | 10 ++++++++--
>  tools/perf/util/branch.c              |  8 +++++++-
>  4 files changed, 29 insertions(+), 6 deletions(-)
> 
> diff --git a/drivers/perf/arm_pmu_brbe.c b/drivers/perf/arm_pmu_brbe.c
> index 8d27ad868359..7cd1208c6c58 100644
> --- a/drivers/perf/arm_pmu_brbe.c
> +++ b/drivers/perf/arm_pmu_brbe.c
> @@ -253,12 +253,17 @@ static int brbe_fetch_perf_type(u64 brbinf)
>  	case BRBINF_TYPE_DEBUG_EXIT:
>  		return PERF_BR_DEBUG_EXIT;
>  	case BRBINF_TYPE_SERROR:
> +		return PERF_BR_SERROR;
>  	case BRBINF_TYPE_INST_DEBUG:
> +		return PERF_BR_DEBUG_INST;
>  	case BRBINF_TYPE_DATA_DEBUG:
> +		return PERF_BR_DEBUG_DATA;
>  	case BRBINF_TYPE_ALGN_FAULT:
> +		return PERF_BR_FAULT_ALGN;
>  	case BRBINF_TYPE_INST_FAULT:
> +		return PERF_BR_FAULT_INST;
>  	case BRBINF_TYPE_DATA_FAULT:
> -		return PERF_BR_UNKNOWN;
> +		return PERF_BR_FAULT_DATA;
>  	default:
>  		pr_warn("unknown branch type captured\n");
>  		return PERF_BR_UNKNOWN;
> diff --git a/include/uapi/linux/perf_event.h b/include/uapi/linux/perf_event.h
> index b91d0f575d0c..361fdc6b87a0 100644
> --- a/include/uapi/linux/perf_event.h
> +++ b/include/uapi/linux/perf_event.h
> @@ -256,6 +256,12 @@ enum {
>  	PERF_BR_FIQ		= 13,	/* fiq */
>  	PERF_BR_DEBUG_HALT	= 14,	/* debug halt */
>  	PERF_BR_DEBUG_EXIT	= 15,	/* debug exit */
> +	PERF_BR_DEBUG_INST	= 16,	/* instruciton debug */
> +	PERF_BR_DEBUG_DATA	= 17,	/* data debug */
> +	PERF_BR_FAULT_ALGN	= 18,	/* alignment fault */
> +	PERF_BR_FAULT_DATA	= 19,	/* data fault */
> +	PERF_BR_FAULT_INST	= 20,	/* instruction fault */
> +	PERF_BR_SERROR		= 21,	/* system error */
>  	PERF_BR_MAX,
>  };
>  
> @@ -1370,8 +1376,8 @@ struct perf_branch_entry {
>  		in_tx:1,    /* in transaction */
>  		abort:1,    /* transaction abort */
>  		cycles:16,  /* cycle count to last branch */
> -		type:4,     /* branch type */
> -		reserved:40;
> +		type:6,     /* branch type */
> +		reserved:38;
>  };
>  
>  union perf_sample_weight {
> diff --git a/tools/include/uapi/linux/perf_event.h b/tools/include/uapi/linux/perf_event.h
> index 1882054e8684..9a82b8aaed93 100644
> --- a/tools/include/uapi/linux/perf_event.h
> +++ b/tools/include/uapi/linux/perf_event.h
> @@ -256,6 +256,12 @@ enum {
>  	PERF_BR_FIQ		= 13,	/* fiq */
>  	PERF_BR_DEBUG_HALT	= 14,	/* debug halt */
>  	PERF_BR_DEBUG_EXIT	= 15,	/* debug exit */
> +	PERF_BR_DEBUG_INST	= 16,	/* instruciton debug */
> +	PERF_BR_DEBUG_DATA	= 17,	/* data debug */
> +	PERF_BR_FAULT_ALGN	= 18,	/* alignment fault */
> +	PERF_BR_FAULT_DATA	= 19,	/* data fault */
> +	PERF_BR_FAULT_INST	= 20,	/* instruction fault */
> +	PERF_BR_SERROR		= 21,	/* system error */
>  	PERF_BR_MAX,
>  };
>  
> @@ -1370,8 +1376,8 @@ struct perf_branch_entry {
>  		in_tx:1,    /* in transaction */
>  		abort:1,    /* transaction abort */
>  		cycles:16,  /* cycle count to last branch */
> -		type:4,     /* branch type */
> -		reserved:40;
> +		type:6,     /* branch type */
> +		reserved:38;
>  };

There's another copy of this struct in branch.h that is used to access the same data in
perf which also needs updating:

	struct branch_flags {
		union {
			u64 value;
			struct {
				u64 mispred:1;
				u64 predicted:1;
				u64 in_tx:1;
				u64 abort:1;
				u64 cycles:16;
				u64 type:4;
				u64 reserved:40;
			};
		};
	};

It's never assigned directly but there is some casting stuff going on in
evsel__parse_sample() and it eventually ends up being used to access branch
records. Same applies to the privilege data change.

>  
>  union perf_sample_weight {
> diff --git a/tools/perf/util/branch.c b/tools/perf/util/branch.c
> index 74e5e67b1779..1e216ea2e2a8 100644
> --- a/tools/perf/util/branch.c
> +++ b/tools/perf/util/branch.c
> @@ -54,7 +54,13 @@ const char *branch_type_name(int type)
>  		"IRQ",
>  		"FIQ",
>  		"DEBUG_HALT",
> -		"DEBUG_EXIT"
> +		"DEBUG_EXIT",
> +		"DEBUG_INST",
> +		"DEBUG_DATA",
> +		"FAULT_ALGN",
> +		"FAULT_DATA",
> +		"FAULT_INST",
> +		"SERROR"
>  	};
>  
>  	if (type >= 0 && type < PERF_BR_MAX)
>