When scheduling a group of events, there are constraint checks done to
make sure all events can go in a group. Example, one of the criteria is
that events in a group cannot use the same PMC. But platform specific
PMU supports alternative event for some of the event codes. During
perf_event_open(), if any event group doesn't match constraint check
criteria, further lookup is done to find alternative event.

By current design, the array of alternatives events in PMU code is
expected to be sorted by column 0. This is because in
find_alternative() the return criteria is based on event code
comparison. ie. "event < ev_alt[i][0])". This optimisation is there
since find_alternative() can be called multiple times. In power9 PMU
code, the alternative event array is not sorted properly and hence there
is breakage in finding alternative events.

To work with existing logic, fix the alternative event array to be
sorted by column 0 for power9-pmu.c

Results:

With alternative events, multiplexing can be avoided. That is, for
example, in power9 PM_LD_MISS_L1 (0x3e054) has alternative event,
PM_LD_MISS_L1_ALT (0x400f0). This is an identical event which can be
programmed in a different PMC.

Before:

 # perf stat -e r3e054,r300fc

 Performance counter stats for 'system wide':

           1057860      r3e054              (50.21%)
               379      r300fc              (49.79%)

       0.944329741 seconds time elapsed

Since both the events are using PMC3 in this case, they are
multiplexed here.

After:

 # perf stat -e r3e054,r300fc

 Performance counter stats for 'system wide':

           1006948      r3e054
               182      r300fc

Fixes: 91e0bd1e ("powerpc/perf: Add PM_LD_MISS_L1 and PM_BR_2PATH to power9 event list")
Signed-off-by: Athira Rajeev <atrajeev@linux.vnet.ibm.com>
Reviewed-by: Madhavan Srinivasan <maddy@linux.vnet.ibm.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20220419114828.89843-1-atrajeev@linux.vnet.ibm.com