Re: [PATCH 2/2] perf header: Additional note on AMD IBS for max_precise pmu cap

[Arnaldo Carvalho de Melo]

Em Tue, Nov 07, 2023 at 02:03:31PM +0530, Ravi Bangoria escreveu:
> From: Arnaldo Carvalho de Melo <acme@xxxxxxxxxx>

Applied this one, waiting for some more time to address Ian comments,

- Arnaldo
 
> x86 core pmu exposes supported maximum precision level via max_precise
> pmu capability. Although, AMD core pmu does not support precise mode,
> certain core pmu events with precise_ip > 0 are allowed and forwarded
> to IBS OP pmu. Display a note about this in perf report header and
> document the details in the perf-list man page.
> 
> Signed-off-by: Arnaldo Carvalho de Melo <acme@xxxxxxxxxx>
> Signed-off-by: Ravi Bangoria <ravi.bangoria@xxxxxxx>
> ---
>  tools/perf/Documentation/perf-list.txt | 12 +++++++-----
>  tools/perf/util/env.c                  | 18 ++++++++++++++++++
>  tools/perf/util/env.h                  |  2 ++
>  tools/perf/util/header.c               |  8 ++++++++
>  4 files changed, 35 insertions(+), 5 deletions(-)
> 
> diff --git a/tools/perf/Documentation/perf-list.txt b/tools/perf/Documentation/perf-list.txt
> index d5f78e125efe..1b90575ee3c8 100644
> --- a/tools/perf/Documentation/perf-list.txt
> +++ b/tools/perf/Documentation/perf-list.txt
> @@ -81,11 +81,13 @@ For Intel systems precise event sampling is implemented with PEBS
>  which supports up to precise-level 2, and precise level 3 for
>  some special cases
>  
> -On AMD systems it is implemented using IBS (up to precise-level 2).
> -The precise modifier works with event types 0x76 (cpu-cycles, CPU
> -clocks not halted) and 0xC1 (micro-ops retired). Both events map to
> -IBS execution sampling (IBS op) with the IBS Op Counter Control bit
> -(IbsOpCntCtl) set respectively (see the
> +On AMD systems it is implemented using IBS OP (up to precise-level 2).
> +Unlike Intel PEBS which provides levels of precision, AMD core pmu is
> +inherently non-precise and IBS is inherently precise. (i.e. ibs_op//,
> +ibs_op//p, ibs_op//pp and ibs_op//ppp are all same). The precise modifier
> +works with event types 0x76 (cpu-cycles, CPU clocks not halted) and 0xC1
> +(micro-ops retired). Both events map to IBS execution sampling (IBS op)
> +with the IBS Op Counter Control bit (IbsOpCntCtl) set respectively (see the
>  Core Complex (CCX) -> Processor x86 Core -> Instruction Based Sampling (IBS)
>  section of the [AMD Processor Programming Reference (PPR)] relevant to the
>  family, model and stepping of the processor being used).
> diff --git a/tools/perf/util/env.c b/tools/perf/util/env.c
> index 44140b7f596a..cbc18b22ace5 100644
> --- a/tools/perf/util/env.c
> +++ b/tools/perf/util/env.c
> @@ -531,6 +531,24 @@ int perf_env__numa_node(struct perf_env *env, struct perf_cpu cpu)
>  	return cpu.cpu >= 0 && cpu.cpu < env->nr_numa_map ? env->numa_map[cpu.cpu] : -1;
>  }
>  
> +bool perf_env__has_pmu_mapping(struct perf_env *env, const char *pmu_name)
> +{
> +	char *pmu_mapping = env->pmu_mappings, *colon;
> +
> +	for (int i = 0; i < env->nr_pmu_mappings; ++i) {
> +		if (strtoul(pmu_mapping, &colon, 0) == ULONG_MAX || *colon != ':')
> +			goto out_error;
> +
> +		pmu_mapping = colon + 1;
> +		if (strcmp(pmu_mapping, pmu_name) == 0)
> +			return true;
> +
> +		pmu_mapping += strlen(pmu_mapping) + 1;
> +	}
> +out_error:
> +	return false;
> +}
> +
>  char *perf_env__find_pmu_cap(struct perf_env *env, const char *pmu_name,
>  			     const char *cap)
>  {
> diff --git a/tools/perf/util/env.h b/tools/perf/util/env.h
> index 4566c51f2fd9..56aea562c61b 100644
> --- a/tools/perf/util/env.h
> +++ b/tools/perf/util/env.h
> @@ -174,4 +174,6 @@ struct btf_node *perf_env__find_btf(struct perf_env *env, __u32 btf_id);
>  int perf_env__numa_node(struct perf_env *env, struct perf_cpu cpu);
>  char *perf_env__find_pmu_cap(struct perf_env *env, const char *pmu_name,
>  			     const char *cap);
> +
> +bool perf_env__has_pmu_mapping(struct perf_env *env, const char *pmu_name);
>  #endif /* __PERF_ENV_H */
> diff --git a/tools/perf/util/header.c b/tools/perf/util/header.c
> index e86b9439ffee..3cc288d14002 100644
> --- a/tools/perf/util/header.c
> +++ b/tools/perf/util/header.c
> @@ -2145,6 +2145,14 @@ static void print_pmu_caps(struct feat_fd *ff, FILE *fp)
>  		__print_pmu_caps(fp, pmu_caps->nr_caps, pmu_caps->caps,
>  				 pmu_caps->pmu_name);
>  	}
> +
> +	if (strcmp(perf_env__arch(&ff->ph->env), "x86") == 0 &&
> +	    perf_env__has_pmu_mapping(&ff->ph->env, "ibs_op")) {
> +		char *max_precise = perf_env__find_pmu_cap(&ff->ph->env, "cpu", "max_precise");
> +
> +		if (max_precise != NULL && atoi(max_precise) == 0)
> +			fprintf(fp, "# AMD systems uses ibs_op// PMU for some precise events, e.g.: cycles:p, see the 'perf list' man page for further details.\n");
> +	}
>  }
>  
>  static void print_pmu_mappings(struct feat_fd *ff, FILE *fp)
> -- 
> 2.41.0
> 

-- 

- Arnaldo