From c6cc9a852f123301d5271f1484df8e961b2b64f1 Mon Sep 17 00:00:00 2001

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

Date: Tue, 19 Apr 2022 17:18:28 +0530

Subject: [PATCH] powerpc/perf: Fix power10 event alternatives

References: jsc#SLE-13513 git-fixes

Patch-mainline: v5.18-rc4

Git-commit: c6cc9a852f123301d5271f1484df8e961b2b64f1

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 power10 PMU

code, the alternative event array is not sorted properly 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 power10-pmu.c

Results:

In case where an alternative event is not chosen when we could, events

will be multiplexed. ie, time sliced where it could actually run

concurrently.

Example, in power10 PM_INST_CMPL_ALT(0x00002) has alternative event,

PM_INST_CMPL(0x500fa). Without the fix, if a group of events with PMC1

to PMC4 is used along with PM_INST_CMPL_ALT, it will be time sliced

since all programmable PMC's are consumed already. But with the fix,

when it picks alternative event on PMC5, all events will run

concurrently.

Before:

 # perf stat -e r00002,r100fc,r200fa,r300fc,r400fc

 Performance counter stats for 'system wide':

         328668935      r00002               (79.94%)

          56501024      r100fc               (79.95%)

          49564238      r200fa               (79.95%)

               376      r300fc               (80.19%)

               660      r400fc               (79.97%)

       4.039150522 seconds time elapsed

With the fix, since alternative event is chosen to run on PMC6, events

will be run concurrently.

After:

 # perf stat -e r00002,r100fc,r200fa,r300fc,r400fc

 Performance counter stats for 'system wide':

          23596607      r00002

           4907738      r100fc

           2283608      r200fa

               135      r300fc

               248      r400fc

       1.664671390 seconds time elapsed

Fixes: a64e697cef23 ("powerpc/perf: power10 Performance Monitoring support")

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/20220419114828.89843-2-atrajeev@linux.vnet.ibm.com

Acked-by: Michal Suchanek <msuchanek@suse.de>

Acked-by: Michal Suchanek <msuchanek@suse.de>

---

 arch/powerpc/perf/power10-pmu.c | 2 +-

 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/arch/powerpc/perf/power10-pmu.c b/arch/powerpc/perf/power10-pmu.c

index d3398100a60f..c6d51e7093cf 100644

--- a/arch/powerpc/perf/power10-pmu.c

+++ b/arch/powerpc/perf/power10-pmu.c

@@ -91,8 +91,8 @@ extern u64 PERF_REG_EXTENDED_MASK;

 /* Table of alternatives, sorted by column 0 */

 static const unsigned int power10_event_alternatives[][MAX_ALT] = {

-	{ PM_CYC_ALT,			PM_CYC },

 	{ PM_INST_CMPL_ALT,		PM_INST_CMPL },

+	{ PM_CYC_ALT,			PM_CYC },

 };

 static int power10_get_alternatives(u64 event, unsigned int flags, u64 alt[])

-- 

2.34.1