[PATCH V3 1/2] powerpc/perf: Fix the power9 event alternatives array to have correct sort order

[Athira Rajeev]

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 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() function, the return criteria is based on
event code comparison. ie "event < ev_alt[i][0])". This
optimisation is there since find_alternative() can get called
multiple times. In power9 PMU code, the alternative event array
is not sorted list and hence there is breakage in finding
alternative event.

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 patch >>

 # perf stat -e r3e054,r300fc
^C
 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.

<<With patch>>

 # perf stat -e r3e054,r300fc
^C
 Performance counter stats for 'system wide':

           1006948      r3e054
               182      r300fc
<<>>

Fixes: 91e0bd1e6251 ("powerpc/perf: Add PM_LD_MISS_L1 and PM_BR_2PATH to power9 event list")
Signed-off-by: Athira Rajeev <atrajeev at linux.vnet.ibm.com>
Reviewed-by: Madhavan Srinivasan <maddy at linux.vnet.ibm.com>
---
Changelog:
 v1 -> v2:
 Added Fixes tag and reworded commit message.
 Added Reviewed-by from Maddy.
 v2 -> v3:
 Added info about what is the breakage with current
 code.

 arch/powerpc/perf/power9-pmu.c | 8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

diff --git a/arch/powerpc/perf/power9-pmu.c b/arch/powerpc/perf/power9-pmu.c
index c9eb5232e68b..c393e837648e 100644
--- a/arch/powerpc/perf/power9-pmu.c
+++ b/arch/powerpc/perf/power9-pmu.c
@@ -133,11 +133,11 @@ int p9_dd22_bl_ev[] = {
 
 /* Table of alternatives, sorted by column 0 */
 static const unsigned int power9_event_alternatives[][MAX_ALT] = {
-	{ PM_INST_DISP,			PM_INST_DISP_ALT },
-	{ PM_RUN_CYC_ALT,		PM_RUN_CYC },
-	{ PM_RUN_INST_CMPL_ALT,		PM_RUN_INST_CMPL },
-	{ PM_LD_MISS_L1,		PM_LD_MISS_L1_ALT },
 	{ PM_BR_2PATH,			PM_BR_2PATH_ALT },
+	{ PM_INST_DISP,			PM_INST_DISP_ALT },
+	{ PM_RUN_CYC_ALT,               PM_RUN_CYC },
+	{ PM_LD_MISS_L1,                PM_LD_MISS_L1_ALT },
+	{ PM_RUN_INST_CMPL_ALT,         PM_RUN_INST_CMPL },
 };
 
 static int power9_get_alternatives(u64 event, unsigned int flags, u64 alt[])
-- 
2.35.1