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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: 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/20200319202517.23423-16-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 13:25:15 -07:00 committed by Arnaldo Carvalho de Melo
parent 680d125cd5
commit 13e0c844fa
3 changed files with 21 additions and 0 deletions
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9
tools/perf/Documentation/perf-top.txt
View File

@ -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
--------------------------

11
tools/perf/builtin-top.c
View File

@ -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;

1
tools/perf/util/top.h
View File

@ -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;