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From:   Sasha Levin <Alexander.Levin@microsoft.com>
To:     "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        "stable@vger.kernel.org" <stable@vger.kernel.org>
CC:     Borislav Petkov <bp@suse.de>,
        Peter Zijlstra <peterz@infradead.org>,
        Robert Richter <rric@kernel.org>,
        Vince Weaver <vince@deater.net>,
        Arnaldo Carvalho de Melo <acme@redhat.com>,
        Sasha Levin <Alexander.Levin@microsoft.com>
Subject: [PATCH AUTOSEL for 4.9 004/219] perf stat: Issue a HW watchdog
 disable hint
Thread-Topic: [PATCH AUTOSEL for 4.9 004/219] perf stat: Issue a HW watchdog
 disable hint
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Date:   Sat, 3 Mar 2018 22:27:57 +0000
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From: Borislav Petkov <bp@suse.de>

[ Upstream commit 02d492e5dcb72c004d213756eb87c9d62a6d76a7 ]

When using perf stat on an AMD F15h system with the default hw events
attributes, some of the events don't get counted:

 Performance counter stats for 'sleep 1':

          0.749208      task-clock (msec)         #    0.001 CPUs utilized
                 1      context-switches          #    0.001 M/sec
                 0      cpu-migrations            #    0.000 K/sec
                54      page-faults               #    0.072 M/sec
         1,122,815      cycles                    #    1.499 GHz
           286,740      stalled-cycles-frontend   #   25.54% frontend cycle=
s idle
     <not counted>      stalled-cycles-backend                             =
           (0.00%)
     ^^^^^^^^^^^^
     <not counted>      instructions                                       =
           (0.00%)
     ^^^^^^^^^^^^
     <not counted>      branches                                           =
           (0.00%)
     <not counted>      branch-misses                                      =
           (0.00%)

       1.001550070 seconds time elapsed

The reason is that we have the HW watchdog consuming one PMU counter and
when perf tries to schedule 6 events on 6 counters and some of those
counters are constrained to only a specific subset of PMCs by the
hardware, the event scheduling fails.

So issue a hint to disable the HW watchdog around a perf stat session.

Committer note:

Testing it...

  # perf stat -d usleep 1

   Performance counter stats for 'usleep 1':

          1.180203      task-clock (msec)         #    0.490 CPUs utilized
                 1      context-switches          #    0.847 K/sec
                 0      cpu-migrations            #    0.000 K/sec
                54      page-faults               #    0.046 M/sec
           184,754      cycles                    #    0.157 GHz
           714,553      instructions              #    3.87  insn per cycle
           154,661      branches                  #  131.046 M/sec
             7,247      branch-misses             #    4.69% of all branche=
s
           219,984      L1-dcache-loads           #  186.395 M/sec
            17,600      L1-dcache-load-misses     #    8.00% of all L1-dcac=
he hits    (90.16%)
     <not counted>      LLC-loads                                          =
           (0.00%)
     <not counted>      LLC-load-misses                                    =
           (0.00%)

       0.002406823 seconds time elapsed

  Some events weren't counted. Try disabling the NMI watchdog:
	echo 0 > /proc/sys/kernel/nmi_watchdog
	perf stat ...
	echo 1 > /proc/sys/kernel/nmi_watchdog
  #

Signed-off-by: Borislav Petkov <bp@suse.de>
Acked-by: Ingo Molnar <mingo@kernel.org>
Tested-by: Arnaldo Carvalho de Melo <acme@redhat.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Robert Richter <rric@kernel.org>
Cc: Vince Weaver <vince@deater.net>
Link: http://lkml.kernel.org/r/20170211183218.ijnvb5f7ciyuunx4@pd.tnic
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>
Signed-off-by: Sasha Levin <alexander.levin@microsoft.com>
---
 tools/perf/builtin-stat.c | 11 +++++++++++
 1 file changed, 11 insertions(+)

diff --git a/tools/perf/builtin-stat.c b/tools/perf/builtin-stat.c
index 688dea7cb08f..c241167c76c9 100644
--- a/tools/perf/builtin-stat.c
+++ b/tools/perf/builtin-stat.c
@@ -146,6 +146,7 @@ static aggr_get_id_t		aggr_get_id;
 static bool			append_file;
 static const char		*output_name;
 static int			output_fd;
+static int			print_free_counters_hint;
=20
 struct perf_stat {
 	bool			 record;
@@ -1109,6 +1110,9 @@ static void printout(int id, int nr, struct perf_evse=
l *counter, double uval,
 			counter->supported ? CNTR_NOT_COUNTED : CNTR_NOT_SUPPORTED,
 			csv_sep);
=20
+		if (counter->supported)
+			print_free_counters_hint =3D 1;
+
 		fprintf(stat_config.output, "%-*s%s",
 			csv_output ? 0 : unit_width,
 			counter->unit, csv_sep);
@@ -1477,6 +1481,13 @@ static void print_footer(void)
 				avg_stats(&walltime_nsecs_stats));
 	}
 	fprintf(output, "\n\n");
+
+	if (print_free_counters_hint)
+		fprintf(output,
+"Some events weren't counted. Try disabling the NMI watchdog:\n"
+"	echo 0 > /proc/sys/kernel/nmi_watchdog\n"
+"	perf stat ...\n"
+"	echo 1 > /proc/sys/kernel/nmi_watchdog\n");
 }
=20
 static void print_counters(struct timespec *ts, int argc, const char **arg=
v)
--=20
2.14.1