linux-kernel - [PATCH 0/5] Don't compute events that won't be used in a metric.

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Date:   Thu, 12 Nov 2020 16:16:46 -0800
From:   Ian Rogers <irogers@...gle.com>
To:     Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...hat.com>,
        Arnaldo Carvalho de Melo <acme@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        Jiri Olsa <jolsa@...hat.com>,
        Namhyung Kim <namhyung@...nel.org>,
        linux-kernel@...r.kernel.org, Andi Kleen <ak@...ux.intel.com>,
        Jin Yao <yao.jin@...ux.intel.com>,
        John Garry <john.garry@...wei.com>,
        Paul Clarke <pc@...ibm.com>, kajoljain <kjain@...ux.ibm.com>
Cc:     Stephane Eranian <eranian@...gle.com>,
        Sandeep Dasgupta <sdasgup@...gle.com>,
        linux-perf-users@...r.kernel.org, Ian Rogers <irogers@...gle.com>
Subject: [PATCH 0/5] Don't compute events that won't be used in a metric.

For a metric like:
  EVENT1 if #smt_on else EVENT2

currently EVENT1 and EVENT2 will be measured and then when the metric
is reported EVENT1 or EVENT2 will be printed depending on the value
from smt_on() during the expr parsing. Computing both events is
unnecessary and can lead to multiplexing as discussed in this thread:
https://lore.kernel.org/lkml/20201110100346.2527031-1-irogers@google.com/

This change modifies expression parsing so that constants are
considered when building the set of ids (events) and only events not
contributing to a constant value are measured.

Ian Rogers (5):
  perf metric: Restructure struct expr_parse_ctx.
  perf metric: Use NAN for missing event IDs.
  perf metric: Rename expr__find_other.
  perf metric: Add utilities to work on ids map.
  perf metric: Don't compute unused events.

 tools/perf/tests/expr.c       | 148 ++++++++++-----
 tools/perf/tests/pmu-events.c |  42 +++--
 tools/perf/util/expr.c        | 136 ++++++++++++--
 tools/perf/util/expr.h        |  17 +-
 tools/perf/util/expr.l        |   9 -
 tools/perf/util/expr.y        | 343 +++++++++++++++++++++++++++-------
 tools/perf/util/metricgroup.c |  44 +++--
 tools/perf/util/stat-shadow.c |  54 ++++--
 8 files changed, 586 insertions(+), 207 deletions(-)

-- 
2.29.2.299.gdc1121823c-goog