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perf c2c: Add option to enable the LBR stitching approach

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With the LBR stitching approach, the reconstructed LBR call stack can
break the HW limitation. However, it may reconstruct invalid call stacks
in some cases, e.g. exception handing such as setjmp/longjmp.  Also, it
may impact the processing time especially when the number of samples
with stitched LBRs are huge.

Add an option to enable the approach.

Signed-off-by: Kan Liang <kan.liang@linux.intel.com>
Reviewed-by: Andi Kleen <ak@linux.intel.com>
Acked-by: Jiri Olsa <jolsa@redhat.com>
Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: Alexey Budankov <alexey.budankov@linux.intel.com>
Cc: Mathieu Poirier <mathieu.poirier@linaro.org>
Cc: Michael Ellerman <mpe@ellerman.id.au>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Pavel Gerasimov <pavel.gerasimov@intel.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Ravi Bangoria <ravi.bangoria@linux.ibm.com>
Cc: Stephane Eranian <eranian@google.com>
Cc: Vitaly Slobodskoy <vitaly.slobodskoy@intel.com>
Link: http://lore.kernel.org/lkml/20200319202517.23423-17-kan.liang@linux.intel.com
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>
This commit is contained in:
Kan Liang 2020-03-19 13:25:16 -07:00 committed by Arnaldo Carvalho de Melo
parent 13e0c844fa
commit d80da766d1
2 changed files with 23 additions and 0 deletions
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11
tools/perf/Documentation/perf-c2c.txt
View file

@ -111,6 +111,17 @@ REPORT OPTIONS
--display::
Switch to HITM type (rmt, lcl) to display and sort on. Total HITMs as default.
--stitch-lbr::
Show callgraph with stitched LBRs, which may have more complete
callgraph. The perf.data file must have been obtained using
perf c2c record --call-graph lbr.
Disabled by default. In common cases with call stack overflows,
it can recreate better call stacks than the default lbr call stack
output. But this approach is not full proof. There can be cases
where it creates incorrect call stacks from incorrect matches.
The known limitations include exception handing such as
setjmp/longjmp will have calls/returns not match.
C2C RECORD
----------
The perf c2c record command setup options related to HITM cacheline analysis

12
tools/perf/builtin-c2c.c
View file

@ -95,6 +95,7 @@ struct perf_c2c {
bool use_stdio;
bool stats_only;
bool symbol_full;
bool stitch_lbr;
/* HITM shared clines stats */
struct c2c_stats hitm_stats;
@ -273,6 +274,9 @@ static int process_sample_event(struct perf_tool *tool __maybe_unused,
return -1;
}
if (c2c.stitch_lbr)
al.thread->lbr_stitch_enable = true;
ret = sample__resolve_callchain(sample, &callchain_cursor, NULL,
evsel, &al, sysctl_perf_event_max_stack);
if (ret)
@ -2601,6 +2605,12 @@ static int setup_callchain(struct evlist *evlist)
}
}
if (c2c.stitch_lbr && (mode != CALLCHAIN_LBR)) {
ui__warning("Can't find LBR callchain. Switch off --stitch-lbr.\n"
"Please apply --call-graph lbr when recording.\n");
c2c.stitch_lbr = false;
}
callchain_param.record_mode = mode;
callchain_param.min_percent = 0;
return 0;
@ -2752,6 +2762,8 @@ static int perf_c2c__report(int argc, const char **argv)
OPT_STRING('c', "coalesce", &coalesce, "coalesce fields",
"coalesce fields: pid,tid,iaddr,dso"),
OPT_BOOLEAN('f', "force", &symbol_conf.force, "don't complain, do it"),
OPT_BOOLEAN(0, "stitch-lbr", &c2c.stitch_lbr,
"Enable LBR callgraph stitching approach"),
OPT_PARENT(c2c_options),
OPT_END()
};