[PATCH v4 0/5] Don't compute events that won't be used in a metric.

Ian Rogers
2020-12-02T06:27:49Z

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.

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
condition.

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 | 136 +++++++++--
tools/perf/util/expr.h | 17 +-
tools/perf/util/expr.l | 9 -
tools/perf/util/expr.y | 418 +++++++++++++++++++++++++++-------
tools/perf/util/metricgroup.c | 44 ++--
tools/perf/util/stat-shadow.c | 54 +++--
8 files changed, 658 insertions(+), 221 deletions(-)

--
2.29.2.454.gaff20da3a2-goog