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Date:   Thu, 23 Sep 2021 00:46:03 -0700
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 v9 00/13] 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.

v9. adds a missing memory allocation failure check in the pmu-metrics
    test.  A memory allocation failure in union returns NULL. Some
    parser debug on IDs is removed. "Modify code layout" is broken
    apart into 3 changes.  "Don't compute unused events" is broken
    apart into 4 changes with the tests merged into the change that
    adds the corresponding optimization. This is trying to address
    feedback from Jiri Olsa <>.  The unmodified
    patches have Reviewed-by: Andi Kleen <> added,
    although the overall patch set is largely the same as v8 which was
    fully reviewed-by.

v8. rebases, adds an ability to compute metrics with no events and
    further breaks apart the "Don't compute unused events" part of the
    change as requested by Jiri Olsa <>.

v7. fixes the fix to be in the correct patch.

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 (13):
  perf metric: Restructure struct expr_parse_ctx.
  perf metric: Use NAN for missing event IDs.
  perf expr: Remove unused headers and inline d_ratio
  perf expr: Separate token declataion from type
  perf expr: Use macros for operators
  perf expr: Move actions to the left.
  perf metric: Rename expr__find_other.
  perf metric: Add utilities to work on ids map.
  perf metric: Allow metrics with no events
  perf expr: Merge find_ids and regular parsing
  perf expr: Propagate constants for binary operations
  perf metric: Don't compute unused events
  perf metric: Avoid events for an 'if' constant result

 tools/perf/tests/expr.c       | 160 ++++++++++++-----
 tools/perf/tests/pmu-events.c |  54 +++---
 tools/perf/util/expr.c        | 121 +++++++++++--
 tools/perf/util/expr.h        |  20 ++-
 tools/perf/util/expr.l        |   9 -
 tools/perf/util/expr.y        | 325 +++++++++++++++++++++++++---------
 tools/perf/util/metricgroup.c | 145 ++++++++-------
 tools/perf/util/stat-shadow.c |  54 +++---
 8 files changed, 620 insertions(+), 268 deletions(-)


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