perf doc: Refresh topdown documentation

perf stat now supports --topdown for any platform with the TopdownL1
metric group including Intel before Icelake. Tweak the documentation
to reflect this.

Signed-off-by: Ian Rogers <irogers@google.com>
Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Cc: Alexandre Torgue <alexandre.torgue@foss.st.com>
Cc: Andrii Nakryiko <andrii@kernel.org>
Cc: Athira Rajeev <atrajeev@linux.vnet.ibm.com>
Cc: Caleb Biggers <caleb.biggers@intel.com>
Cc: Eduard Zingerman <eddyz87@gmail.com>
Cc: Florian Fischer <florian.fischer@muhq.space>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: James Clark <james.clark@arm.com>
Cc: Jing Zhang <renyu.zj@linux.alibaba.com>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: John Garry <john.g.garry@oracle.com>
Cc: Kajol Jain <kjain@linux.ibm.com>
Cc: Kan Liang <kan.liang@linux.intel.com>
Cc: Leo Yan <leo.yan@linaro.org>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Maxime Coquelin <mcoquelin.stm32@gmail.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Perry Taylor <perry.taylor@intel.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Ravi Bangoria <ravi.bangoria@amd.com>
Cc: Sandipan Das <sandipan.das@amd.com>
Cc: Sean Christopherson <seanjc@google.com>
Cc: Stephane Eranian <eranian@google.com>
Cc: Suzuki Poulouse <suzuki.poulose@arm.com>
Cc: Xing Zhengjun <zhengjun.xing@linux.intel.com>
Cc: linux-arm-kernel@lists.infradead.org
Cc: linux-stm32@st-md-mailman.stormreply.com
Link: https://lore.kernel.org/r/20230219092848.639226-43-irogers@google.com
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

1 files changed, 15 insertions, 12 deletions

diff --git a/tools/perf/Documentation/perf-stat.txt b/tools/perf/Documentation/perf-stat.txt
index 18abdc1dce05..29bdcfa93f04 100644
--- a/tools/perf/Documentation/perf-stat.txt
+++ b/tools/perf/Documentation/perf-stat.txt
@@ -394,10 +394,10 @@ See perf list output for the possible metrics and metricgroups.
 Do not aggregate counts across all monitored CPUs.
 
 --topdown::
-Print complete top-down metrics supported by the CPU. This allows to
-determine bottle necks in the CPU pipeline for CPU bound workloads,
-by breaking the cycles consumed down into frontend bound, backend bound,
-bad speculation and retiring.
+Print top-down metrics supported by the CPU. This allows to determine
+bottle necks in the CPU pipeline for CPU bound workloads, by breaking
+the cycles consumed down into frontend bound, backend bound, bad
+speculation and retiring.
 
 Frontend bound means that the CPU cannot fetch and decode instructions fast
 enough. Backend bound means that computation or memory access is the bottle
@@ -430,15 +430,18 @@ CPUs the workload runs on. If needed the CPUs can be forced using
 taskset.
 
 --td-level::
-Print the top-down statistics that equal to or lower than the input level.
-It allows users to print the interested top-down metrics level instead of
-the complete top-down metrics.
+Print the top-down statistics that equal the input level. It allows
+users to print the interested top-down metrics level instead of the
+level 1 top-down metrics.
+
+As the higher levels gather more metrics and use more counters they
+will be less accurate. By convention a metric can be examined by
+appending '_group' to it and this will increase accuracy compared to
+gathering all metrics for a level. For example, level 1 analysis may
+highlight 'tma_frontend_bound'. This metric may be drilled into with
+'tma_frontend_bound_group' with
+'perf stat -M tma_frontend_bound_group...'.
 
-The availability of the top-down metrics level depends on the hardware. For
-example, Ice Lake only supports L1 top-down metrics. The Sapphire Rapids
-supports both L1 and L2 top-down metrics.
-
-Default: 0 means the max level that the current hardware support.
 Error out if the input is higher than the supported max level.
 
 --no-merge::