perf report: Add option to enable the LBR stitching approach

Kan Liang · acmel · commit b1d1429b1820 · 2020-04-18T09:05:01.000-03:00
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. # To display the perf.data header info, please use # --header/--header-only options. # # # Total Lost Samples: 0 # # Samples: 6K of event 'cycles' # Event count (approx.): 6492797701 # # Children Self Command Shared Object Symbol # ........ ........ ............... .................. # ................................. # 99.99% 99.99% tchain_edit tchain_edit [.] f43 | ---main f1 f2 f3 f4 f5 f6 f7 f8 f9 f10 f11 f12 f13 f14 f15 f16 f17 f18 f19 f20 f21 f22 f23 f24 f25 f26 f27 f28 f29 f30 f31 | --99.65%--f32 f33 f34 f35 f36 f37 f38 f39 f40 f41 f42 f43 Committer testing: $ perf record --call-graph lbr /wb/tchain_edit [ perf record: Woken up 23 times to write data ] [ perf record: Captured and wrote 5.578 MB perf.data (6839 samples) ] $ perf report --header-only | egrep 'cpu(desc|.*capabilities)' # cpudesc : Intel(R) Core(TM) i5-7500 CPU @ 3.40GHz # cpu pmu capabilities: branches=32, max_precise=3, pmu_name=skylake $ Before: $ perf report --no-children --stdio # To display the perf.data header info, please use --header/--header-only options. # # # Total Lost Samples: 0 # # Samples: 6K of event 'cycles:u' # Event count (approx.): 6459523879 # # Overhead Command Shared Object Symbol # ........ ........... ................ ....................... # 99.95% tchain_edit tchain_edit [.] f43 | --99.92%--f43 f42 f41 f40 f39 f38 f37 f36 f35 f34 f33 f32 f31 f30 f29 f28 f27 f26 f25 f24 f23 f22 f21 f20 f19 f18 f17 f16 f15 f14 f13 f12 f11 0.03% tchain_edit tchain_edit [.] f42 0.01% tchain_edit tchain_edit [.] f41 0.00% tchain_edit tchain_edit [.] f31 0.00% tchain_edit ld-2.29.so [.] _dl_relocate_object 0.00% tchain_edit ld-2.29.so [.] memmove 0.00% tchain_edit [unknown] [k] 0xffffffff93a00b17 After: $ perf report --stitch-lbr --no-children --stdio # To display the perf.data header info, please use --header/--header-only options. # # # Total Lost Samples: 0 # # Samples: 6K of event 'cycles:u' # Event count (approx.): 6459496645 # # Overhead Command Shared Object Symbol # ........ ........... ................ ........................ # 99.97% tchain_edit tchain_edit [.] f43 | --99.93%--f43 f42 f41 f40 f39 f38 f37 f36 f35 f34 f33 f32 f31 f30 f29 f28 f27 f26 f25 f24 f23 f22 f21 f20 f19 f18 f17 f16 f15 f14 f13 f12 f11 f10 f9 f8 f7 f6 f5 f4 f3 f2 f1 main __libc_start_main 0.02% tchain_edit [unknown] [k] 0xffffffff93a00b17 0.01% tchain_edit tchain_edit [.] f31 0.00% tchain_edit ld-2.29.so [.] _dl_important_hwcaps 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> Tested-by: Arnaldo Carvalho de Melo <acme@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/20200319202517.23423-14-kan.liang@linux.intel.com Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>
diff --git a/tools/perf/Documentation/perf-report.txt b/tools/perf/Documentation/perf-report.txt
@@ -488,6 +488,17 @@ include::itrace.txt[]
 	This option extends the perf report to show reference callgraphs,
 	which collected by reference event, in no callgraph event.
 
+--stitch-lbr::
+	Show callgraph with stitched LBRs, which may have more complete
+	callgraph. The perf.data file must have been obtained using
+	perf 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.
+
 --socket-filter::
 	Only report the samples on the processor socket that match with this filter
 
diff --git a/tools/perf/builtin-report.c b/tools/perf/builtin-report.c
@@ -84,6 +84,7 @@ struct report {
 	bool			header_only;
 	bool			nonany_branch_mode;
 	bool			group_set;
+	bool			stitch_lbr;
 	int			max_stack;
 	struct perf_read_values	show_threads_values;
 	struct annotation_options annotation_opts;
@@ -267,6 +268,9 @@ static int process_sample_event(struct perf_tool *tool,
 		return -1;
 	}
 
+	if (rep->stitch_lbr)
+		al.thread->lbr_stitch_enable = true;
+
 	if (symbol_conf.hide_unresolved && al.sym == NULL)
 		goto out_put;
 
@@ -408,6 +412,12 @@ static int report__setup_sample_type(struct report *rep)
 			callchain_param.record_mode = CALLCHAIN_FP;
 	}
 
+	if (rep->stitch_lbr && (callchain_param.record_mode != CALLCHAIN_LBR)) {
+		ui__warning("Can't find LBR callchain. Switch off --stitch-lbr.\n"
+			    "Please apply --call-graph lbr when recording.\n");
+		rep->stitch_lbr = false;
+	}
+
 	/* ??? handle more cases than just ANY? */
 	if (!(perf_evlist__combined_branch_type(session->evlist) &
 				PERF_SAMPLE_BRANCH_ANY))
@@ -1258,6 +1268,8 @@ int cmd_report(int argc, const char **argv)
 			"Show full source file name path for source lines"),
 	OPT_BOOLEAN(0, "show-ref-call-graph", &symbol_conf.show_ref_callgraph,
 		    "Show callgraph from reference event"),
+	OPT_BOOLEAN(0, "stitch-lbr", &report.stitch_lbr,
+		    "Enable LBR callgraph stitching approach"),
 	OPT_INTEGER(0, "socket-filter", &report.socket_filter,
 		    "only show processor socket that match with this filter"),
 	OPT_BOOLEAN(0, "raw-trace", &symbol_conf.raw_trace,
