[PATCH 5.15 095/124] powerpc/perf: Fix power9 event alternatives

Greg Kroah-Hartman
2022-04-26T09:12:42Z

From: Athira Rajeev <atrajeev@linux.vnet.ibm.com>

[ Upstream commit 0dcad700bb2776e3886fe0a645a4bf13b1e747cd ]

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: 91e0bd1e6251 ("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
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
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 ff3382140d7e..cbdd074ee2a7 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