Patch "perf stat: Issue a HW watchdog disable hint" has been added to the 4.9-stable tree

This is a note to let you know that I've just added the patch titled

perf stat: Issue a HW watchdog disable hint

to the 4.9-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
perf-stat-issue-a-hw-watchdog-disable-hint.patch
and it can be found in the queue-4.9 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let <[email protected]> know about it.

From: Borislav Petkov <[email protected]>
Date: Tue, 7 Feb 2017 01:40:05 +0100
Subject: perf stat: Issue a HW watchdog disable hint

From: Borislav Petkov <[email protected]>

[ 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 cycles 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 branches
           219,984      L1-dcache-loads           #  186.395 M/sec
            17,600      L1-dcache-load-misses     #    8.00% of all L1-dcache 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
#

---
 tools/perf/builtin-stat.c |   11 +++++++++++
 1 file changed, 11 insertions(+)

@@ -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;
 
 struct perf_stat {
 	bool			 record;

@@ -1109,6 +1110,9 @@ static void printout(int id, int nr, str
 			counter->supported ? CNTR_NOT_COUNTED : CNTR_NOT_SUPPORTED,
 			csv_sep);
 
+		if (counter->supported)
+			print_free_counters_hint = 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");
 }
 
 static void print_counters(struct timespec *ts, int argc, const char **argv)

Patches currently in stable-queue which might be from [email protected] are

queue-4.9/x86-mce-handle-broadcasted-mce-gracefully-with-kexec.patch queue-4.9/perf-stat-issue-a-hw-watchdog-disable-hint.patch queue-4.9/x86-mm-make-mmap-map_32bit-work-correctly.patch queue-4.9/edac-altera-fix-peripheral-warnings-for-cyclone5.patch queue-4.9/kvm-svm-setup-mcg_cap-on-amd-properly.patch queue-4.9/x86-mce-init-some-cpu-features-early.patch