Arm PMUs have a suffix, either a single decimal (armv8_pmuv3_0) or 3 hex
digits which (armv8_cortex_a53) which Perf assumes are both strippable
suffixes for the purposes of deduplication. S390 "cpum_cf" is a
similarly suffixed core PMU but is only two characters so is not treated
as strippable because the rules are a minimum of 3 hex characters or 1
decimal character.

There are two paths involved in listing PMU events:

 * HW/cache event printing assumes core PMUs don't have suffixes so
   doesn't try to strip.
 * Sysfs PMU events share the printing function with uncore PMUs which
   strips.

This results in slightly inconsistent Perf list behavior if a core PMU
has a suffix:

  # perf list
  ...
  armv8_pmuv3_0/branch-load-misses/
  armv8_pmuv3/l3d_cache_wb/          [Kernel PMU event]
  ...

Fix it by partially reverting back to the old list behavior where
stripping was only done for uncore PMUs. For example commit 8d9f5146
("perf pmus: Sort pmus by name then suffix") mentions that only PMUs
starting 'uncore_' are considered to have a potential suffix. This
change doesn't go back that far, but does only strip PMUs that are
!is_core. This keeps the desirable behavior where the many possibly
duplicated uncore PMUs aren't repeated, but it doesn't break listing for
core PMUs.

Searching for a PMU continues to use the new stripped comparison
functions, meaning that it's still possible to request an event by
specifying the common part of a PMU name, or even open events on
multiple similarly named PMUs. For example:

  # perf stat -e armv8_cortex/inst_retired/

  5777173628      armv8_cortex_a53/inst_retired/          (99.93%)
  7469626951      armv8_cortex_a57/inst_retired/          (49.88%)

Fixes: 3241d46f ("perf pmus: Sort/merge/aggregate PMUs like mrvl_ddr_pmu")
Suggested-by: Ian Rogers <irogers@google.com>
Signed-off-by: James Clark <james.clark@arm.com>
Reviewed-by: Ian Rogers <irogers@google.com>
Cc: robin.murphy@arm.com
Signed-off-by: Namhyung Kim <namhyung@kernel.org>
Link: https://lore.kernel.org/r/20240626145448.896746-3-james.clark@arm.com