perf metrics: Make common stalled metrics conditional on having the event

The metric code uses the event parsing code but it generally assumes
all events are supported. Arnaldo reported AMD supporting
stalled-cycles-frontend but not stalled-cycles-backend [1]. An issue
with this is that before parsing happens the metric code tries to
share events within groups to reduce the number of events and
multiplexing. If the group has some supported and not supported
events, the whole group will become broken. To avoid this situation
add has_event tests to the metrics for stalled-cycles-frontend and
stalled-cycles-backend. has_events is evaluated when parsing the
metric and its result constant propagated (with if-elses) to reduce
the number of events. This means when the metric code considers
sharing the events, only supported events will be shared.

Note for backporting. This change updates
tools/perf/pmu-events/empty-pmu-events.c a convenience file for builds
on systems without python present. While the metrics.json code should
backport easily there can be conflicts on empty-pmu-events.c. In this
case the build will have left a file test-empty-pmu-events.c that can
be copied over empty-pmu-events.c to resolve issues and make an
appropriate empty-pmu-events.c for the json in the source tree at the
time of the build.

[1] https://lore.kernel.org/lkml/abm1nR-2xjOUBroD@x1/

Reported-by: Arnaldo Carvalho de Melo <acme@kernel.org>
Closes: https://lore.kernel.org/lkml/abm1nR-2xjOUBroD@x1/
Fixes: c7adeb0974f1 ("perf jevents: Add set of common metrics based on default ones")
Signed-off-by: Ian Rogers <irogers@google.com>
Signed-off-by: Namhyung Kim <namhyung@kernel.org>

0 files changed, 0 insertions, 0 deletions