perf pmu: Assume sysfs events are always the same case

Perf event names aren't case sensitive. For sysfs events the entire
directory of events is read then iterated comparing names in a case
insensitive way, most often to see if an event is present.

Consider:

  $ perf stat -e inst_retired.any true

The event inst_retired.any may be present in any PMU, so every PMU's
sysfs events are loaded and then searched with strcasecmp to see if
any match. This event is only present on the cpu PMU as a JSON event
so a lot of events were loaded from sysfs unnecessarily just to prove
an event didn't exist there.

This change avoids loading all the events by assuming sysfs event
names are always either lower or uppercase. It uses file exists and
only loads the events when the desired event is present.

For the example above, the number of openat calls measured by 'perf
trace' on a tigerlake laptop goes from 325 down to 255. The reduction
will be larger for machines with many PMUs, particularly replicated
uncore PMUs.

Ensure pmu_aliases_parse() is called before all uses of the aliases
list, but remove some "pmu->sysfs_aliases_loaded" tests as they are now
part of the function.

Reviewed-by: Kan Liang <[email protected]>
Signed-off-by: Ian Rogers <[email protected]>
Cc: Alexander Shishkin <[email protected]>
Cc: Bjorn Helgaas <[email protected]>
Cc: Ingo Molnar <[email protected]>
Cc: James Clark <[email protected]>
Cc: Jing Zhang <[email protected]>
Cc: Jiri Olsa <[email protected]>
Cc: Jonathan Corbet <[email protected]>
Cc: Mark Rutland <[email protected]>
Cc: Namhyung Kim <[email protected]>
Cc: Peter Zijlstra <[email protected]>
Cc: Randy Dunlap <[email protected]>
Cc: Ravi Bangoria <[email protected]>
Cc: Thomas Richter <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Arnaldo Carvalho de Melo <[email protected]>

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