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The Intel PT decoder limits the number of unconditional branches (e.g.
jmps) decoded without consuming any trace packets. Generally, a loop
needs a conditional branch which generates a TNT packet, whereas a "ret"
instruction will generate a TIP or TNT packet. So exceeding the limit is
assumed to be a never-ending loop, which can happen if there has been a
decoding error putting the decoder at the wrong place in the code.
Up until now, the limit of 10000 has been enough but some analytic
purposes have been reported to exceed that.
Increase the limit to 100000, and make it configurable via perf config
intel-pt.max-loops. Also amend the "Never-ending loop" message to
mention the configuration entry.
Signed-off-by: Adrian Hunter <adrian.hunter@intel.com>
Reviewed-by: Andi Kleen <ak@linux.intel.com>
Cc: Jiri Olsa <jolsa@redhat.com>
Link: http://lore.kernel.org/lkml/20210701175132.3977-1-adrian.hunter@intel.com
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>
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If we run a single workload that only runs on big core, there is always
a ugly message about disabling the NMI watchdog because the atom is not
counted.
Before:
# ./perf stat true
Performance counter stats for 'true':
0.43 msec task-clock # 0.396 CPUs utilized
0 context-switches # 0.000 /sec
0 cpu-migrations # 0.000 /sec
45 page-faults # 103.918 K/sec
639,634 cpu_core/cycles/ # 1.477 G/sec
<not counted> cpu_atom/cycles/ (0.00%)
643,498 cpu_core/instructions/ # 1.486 G/sec
<not counted> cpu_atom/instructions/ (0.00%)
123,715 cpu_core/branches/ # 285.694 M/sec
<not counted> cpu_atom/branches/ (0.00%)
4,094 cpu_core/branch-misses/ # 9.454 M/sec
<not counted> cpu_atom/branch-misses/ (0.00%)
0.001092407 seconds time elapsed
0.001144000 seconds user
0.000000000 seconds sys
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
# ./perf stat -e '{cpu_atom/cycles/,msr/tsc/}' true
Performance counter stats for 'true':
<not counted> cpu_atom/cycles/ (0.00%)
<not counted> msr/tsc/ (0.00%)
0.001904106 seconds time elapsed
0.001947000 seconds user
0.000000000 seconds sys
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
The events in group usually have to be from the same PMU. Try reorganizing the group.
Now we disable the NMI watchdog message on hybrid, otherwise there
are too many false positives.
After:
# ./perf stat true
Performance counter stats for 'true':
0.79 msec task-clock # 0.419 CPUs utilized
0 context-switches # 0.000 /sec
0 cpu-migrations # 0.000 /sec
48 page-faults # 60.889 K/sec
777,692 cpu_core/cycles/ # 986.519 M/sec
<not counted> cpu_atom/cycles/ (0.00%)
669,147 cpu_core/instructions/ # 848.828 M/sec
<not counted> cpu_atom/instructions/ (0.00%)
128,635 cpu_core/branches/ # 163.176 M/sec
<not counted> cpu_atom/branches/ (0.00%)
4,089 cpu_core/branch-misses/ # 5.187 M/sec
<not counted> cpu_atom/branch-misses/ (0.00%)
0.001880649 seconds time elapsed
0.001935000 seconds user
0.000000000 seconds sys
# ./perf stat -e '{cpu_atom/cycles/,msr/tsc/}' true
Performance counter stats for 'true':
<not counted> cpu_atom/cycles/ (0.00%)
<not counted> msr/tsc/ (0.00%)
0.000963319 seconds time elapsed
0.000999000 seconds user
0.000000000 seconds sys
Signed-off-by: Jin Yao <yao.jin@linux.intel.com>
Acked-by: Jiri Olsa <jolsa@kernel.org>
Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Cc: Andi Kleen <ak@linux.intel.com>
Cc: Jin Yao <yao.jin@intel.com>
Cc: Kan Liang <kan.liang@linux.intel.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Link: http://lore.kernel.org/lkml/20210610034557.29766-1-yao.jin@linux.intel.com
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>
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