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Date: Thu, 9 Nov 2023 16:56:15 -0300
From: Arnaldo Carvalho de Melo <acme@...nel.org>
To: Ravi Bangoria <ravi.bangoria@....com>
Cc: namhyung@...nel.org, kim.phillips@....com, peterz@...radead.org,
mingo@...hat.com, mark.rutland@....com,
alexander.shishkin@...ux.intel.com, jolsa@...nel.org,
irogers@...gle.com, adrian.hunter@...el.com,
kan.liang@...ux.intel.com, changbin.du@...wei.com,
yangjihong1@...wei.com, zwisler@...omium.org,
wangming01@...ngson.cn, chenhuacai@...nel.org,
kprateek.nayak@....com, linux-perf-users@...r.kernel.org,
linux-kernel@...r.kernel.org, sandipan.das@....com,
ananth.narayan@....com, santosh.shukla@....com
Subject: Re: [PATCH 2/2] perf header: Additional note on AMD IBS for
max_precise pmu cap
Em Tue, Nov 07, 2023 at 02:03:31PM +0530, Ravi Bangoria escreveu:
> From: Arnaldo Carvalho de Melo <acme@...nel.org>
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@...nel.org>
> Signed-off-by: Ravi Bangoria <ravi.bangoria@....com>
> ---
> 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
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