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Date:   Tue, 12 Jan 2021 14:57:57 -0800
From:   Ian Rogers <>
To:     Peter Zijlstra <>,
        Ingo Molnar <>,
        Arnaldo Carvalho de Melo <>,
        Mark Rutland <>,
        Alexander Shishkin <>,
        Jiri Olsa <>,
        Namhyung Kim <>,, Andi Kleen <>,
        Jin Yao <>,
        John Garry <>,
        Paul Clarke <>, kajoljain <>
Cc:     Stephane Eranian <>,
        Sandeep Dasgupta <>,
        Ian Rogers <>
Subject: [PATCH v6 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:

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.

v6. rebases and fixes issues raised by Namhyung Kim <>,
a memory leak and a function comment.

v5. uses macros to reduce boiler plate in patch 5/5 as suggested by
Andi Kleen <>.

v4. reduces references to BOTTOM/NAN in patch 5/5 by using utility
functions. It improves comments and fixes an unnecessary union in a
peephole optimization.

v3. fixes an assignment in patch 2/5. In patch 5/5 additional comments
are added and useless frees are replaced by asserts. A new peephole
optimization is added for the case CONST IF expr ELSE CONST, where the
the constants are identical, as we don't need to evaluate the IF

v2. is a rebase.

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       | 159 +++++++++++-----
 tools/perf/tests/pmu-events.c |  42 +++--
 tools/perf/util/expr.c        | 137 ++++++++++++--
 tools/perf/util/expr.h        |  21 ++-
 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, 591 insertions(+), 218 deletions(-)


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