Commit 13e0c844 authored by Kan Liang's avatar Kan Liang Committed by Arnaldo Carvalho de Melo
Browse files

perf top: Add option to enable the LBR stitching approach 



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.
The option must be used with --call-graph lbr.

Signed-off-by: default avatarKan Liang <kan.liang@linux.intel.com>
Reviewed-by: default avatarAndi Kleen <ak@linux.intel.com>
Acked-by: default avatarJiri Olsa <jolsa@redhat.com>
Tested-by: default avatarArnaldo 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/20200319202517.23423-16-kan.liang@linux.intel.com


Signed-off-by: default avatarArnaldo Carvalho de Melo <acme@redhat.com>
parent 680d125c

tools/perf/Documentation/perf-top.txt

+9 −0
Original line number Diff line number Diff line
@@ -319,6 +319,15 @@ Default is to monitor all CPUS. 
	go straight to the histogram browser, just like 'perf top' with no events

	explicitely specified does.



--stitch-lbr::

	Show callgraph with stitched LBRs, which may have more complete

	callgraph. The option must be used with --call-graph lbr recording.

	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.



INTERACTIVE PROMPTING KEYS

--------------------------

tools/perf/builtin-top.c

+11 −0
Original line number Diff line number Diff line
@@ -33,6 +33,7 @@ 
#include "util/map.h"

#include "util/mmap.h"

#include "util/session.h"

#include "util/thread.h"

#include "util/symbol.h"

#include "util/synthetic-events.h"

#include "util/top.h"
@@ -775,6 +776,9 @@ static void perf_event__process_sample(struct perf_tool *tool, 
	if (machine__resolve(machine, &al, sample) < 0)

		return;



	if (top->stitch_lbr)

		al.thread->lbr_stitch_enable = true;



	if (!machine->kptr_restrict_warned &&

	    symbol_conf.kptr_restrict &&

	    al.cpumode == PERF_RECORD_MISC_KERNEL) {
@@ -1571,6 +1575,8 @@ int cmd_top(int argc, const char **argv) 
		    "Sort the output by the event at the index n in group. "

		    "If n is invalid, sort by the first event. "

		    "WARNING: should be used on grouped events."),

	OPT_BOOLEAN(0, "stitch-lbr", &top.stitch_lbr,

		    "Enable LBR callgraph stitching approach"),

	OPTS_EVSWITCH(&top.evswitch),

	OPT_END()

	};
@@ -1640,6 +1646,11 @@ int cmd_top(int argc, const char **argv) 
		}

	}



	if (top.stitch_lbr && !(callchain_param.record_mode == CALLCHAIN_LBR)) {

		pr_err("Error: --stitch-lbr must be used with --call-graph lbr\n");

		goto out_delete_evlist;

	}



	if (opts->branch_stack && callchain_param.enabled)

		symbol_conf.show_branchflag_count = true;

tools/perf/util/top.h

+1 −0
Original line number Diff line number Diff line
@@ -36,6 +36,7 @@ struct perf_top { 
	bool		   use_tui, use_stdio;

	bool		   vmlinux_warned;

	bool		   dump_symtab;

	bool		   stitch_lbr;

	struct hist_entry  *sym_filter_entry;

	struct evsel 	   *sym_evsel;

	struct perf_session *session;

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