[RFC PATCH 0/7] Share events between metrics

[Ian Rogers]

Metric groups contain metrics. Metrics create groups of events to
ideally be scheduled together. Often metrics refer to the same events,
for example, a cache hit and cache miss rate. Using separate event
groups means these metrics are multiplexed at different times and the
counts don't sum to 100%. More multiplexing also decreases the
accuracy of the measurement.

This change orders metrics from groups or the command line, so that
the ones with the most events are set up first. Later metrics see if
groups already provide their events, and reuse them if
possible. Unnecessary events and groups are eliminated.

RFC because:
 - without this change events within a metric may get scheduled
   together, after they may appear as part of a larger group and be
   multiplexed at different times, lowering accuracy - however, less
   multiplexing may compensate for this.
 - libbpf's hashmap is used, however, libbpf is an optional
   requirement for building perf.
 - other things I'm not thinking of.

Thanks!

Ian Rogers (7):
  perf expr: migrate expr ids table to libbpf's hashmap
  perf metricgroup: change evlist_used to a bitmap
  perf metricgroup: free metric_events on error
  perf metricgroup: always place duration_time last
  perf metricgroup: delay events string creation
  perf metricgroup: order event groups by size
  perf metricgroup: remove duped metric group events

 tools/perf/tests/expr.c       |  32 ++---
 tools/perf/tests/pmu-events.c |  22 ++--
 tools/perf/util/expr.c        | 125 ++++++++++--------
 tools/perf/util/expr.h        |  22 ++--
 tools/perf/util/expr.y        |  22 +---
 tools/perf/util/metricgroup.c | 242 +++++++++++++++++++++-------------
 tools/perf/util/stat-shadow.c |  46 ++++---
 7 files changed, 280 insertions(+), 231 deletions(-)

-- 
2.26.2.526.g744177e7f7-goog