On Sat, Feb 11, 2017 at 06:59:10PM +0100, Ingo Molnar wrote:
> So I checked the perf-list manpage and it didn't tell me much about how to
> disable
> the NMI watchdog.
Oh, it is buried there:
"
EVENT GROUPS
------------
...
Globally pinned events can limit the number of counters available for
other groups. On x86 systems, the NMI watchdog pins a counter by default.
The nmi watchdog can be disabled as root with
echo 0 > /proc/sys/kernel/nmi_watchdog"
> How about a more proactive hint, something like:
>
> To disable the NMI watchdog permanently, do:
Why permanently? We want it to run and be disabled around the
measurement only. Anyway, here's something more to the point:
---
From: Borislav Petkov <[email protected]>
Date: Tue, 7 Feb 2017 01:40:05 +0100
Subject: [PATCH -v2] perf stat: Issue a HW watchdog disable hint
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.
Signed-off-by: Borislav Petkov <[email protected]>
---
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 a02f2e965628..a2763243a03d 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;
struct perf_stat {
bool record;
@@ -1109,6 +1110,9 @@ static void printout(int id, int nr, struct perf_evsel
*counter, double uval,
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)
--
2.11.0
--
Regards/Gruss,
Boris.
Good mailing practices for 400: avoid top-posting and trim the reply.
