[tip:perf/core] perf tools: Enable LBR call stack support

From: tip-bot for Kan Liang
Date: Wed Feb 18 2015 - 12:19:02 EST

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Commit-ID: aad2b21c151273fa7abc419dac51a980eff1dd17
Gitweb: http://git.kernel.org/tip/aad2b21c151273fa7abc419dac51a980eff1dd17
Author: Kan Liang <kan.liang@xxxxxxxxx>
AuthorDate: Mon, 5 Jan 2015 13:23:04 -0500
Committer: Ingo Molnar <mingo@xxxxxxxxxx>
CommitDate: Wed, 18 Feb 2015 17:16:17 +0100

perf tools: Enable LBR call stack support

Currently, there are two call chain recording options, fp and dwarf.

Haswell has a new feature that utilizes the existing LBR facility to
record call chains. Kernel side LBR support code provides this as a
third option to record call chains. This patch enables the lbr call
stack support on the tooling side.

LBR call stack has some limitations:

- It reuses current LBR facility, so LBR call stack and branch record
can not be enabled at the same time.

- It is only available for user-space callchains.

However, it also offers some advantages:

- LBR call stack can work on user apps which don't have frame-pointers
or dwarf debug info compiled. It is a good alternative when nothing
else works.

Tested-by: Jiri Olsa <jolsa@xxxxxxxxxx>
Signed-off-by: Kan Liang <kan.liang@xxxxxxxxx>
Signed-off-by: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx>
Cc: Adrian Hunter <adrian.hunter@xxxxxxxxx>
Cc: Anshuman Khandual <khandual@xxxxxxxxxxxxxxxxxx>
Cc: Arnaldo Carvalho de Melo <acme@xxxxxxxxxx>
Cc: Cody P Schafer <cody@xxxxxxxxxxxxxxxxxx>
Cc: David Ahern <dsahern@xxxxxxxxx>
Cc: Don Zickus <dzickus@xxxxxxxxxx>
Cc: Jacob Shin <jacob.w.shin@xxxxxxxxx>
Cc: Jiri Olsa <jolsa@xxxxxxxxxx>
Cc: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Cc: Masanari Iida <standby24x7@xxxxxxxxx>
Cc: Namhyung Kim <namhyung@xxxxxxxxxx>
Cc: Paul Mackerras <paulus@xxxxxxxxx>
Cc: Rodrigo Campos <rodrigo@xxxxxxxxxxx>
Cc: Stephane Eranian <eranian@xxxxxxxxxx>
Cc: Sukadev Bhattiprolu <sukadev@xxxxxxxxxxxxxxxxxx>
Link: http://lkml.kernel.org/r/1420482185-29830-2-git-send-email-kan.liang@xxxxxxxxx
Signed-off-by: Ingo Molnar <mingo@xxxxxxxxxx>
---
tools/perf/Documentation/perf-record.txt | 8 +++++++-
tools/perf/builtin-record.c | 6 +++---
tools/perf/builtin-report.c | 2 ++
tools/perf/util/callchain.c | 8 ++++++++
tools/perf/util/callchain.h | 1 +
tools/perf/util/evsel.c | 21 +++++++++++++++++++--
6 files changed, 40 insertions(+), 6 deletions(-)

diff --git a/tools/perf/Documentation/perf-record.txt b/tools/perf/Documentation/perf-record.txt
index 31e9774..1c7e50f 100644
--- a/tools/perf/Documentation/perf-record.txt
+++ b/tools/perf/Documentation/perf-record.txt
@@ -115,13 +115,19 @@ OPTIONS
implies -g.

Allows specifying "fp" (frame pointer) or "dwarf"
- (DWARF's CFI - Call Frame Information) as the method to collect
+ (DWARF's CFI - Call Frame Information) or "lbr"
+ (Hardware Last Branch Record facility) as the method to collect
the information used to show the call graphs.

In some systems, where binaries are build with gcc
--fomit-frame-pointer, using the "fp" method will produce bogus
call graphs, using "dwarf", if available (perf tools linked to
the libunwind library) should be used instead.
+ Using the "lbr" method doesn't require any compiler options. It
+ will produce call graphs from the hardware LBR registers. The
+ main limition is that it is only available on new Intel
+ platforms, such as Haswell. It can only get user call chain. It
+ doesn't work with branch stack sampling at the same time.

-q::
--quiet::
diff --git a/tools/perf/builtin-record.c b/tools/perf/builtin-record.c
index 404ab34..d0d02a8 100644
--- a/tools/perf/builtin-record.c
+++ b/tools/perf/builtin-record.c
@@ -658,7 +658,7 @@ error:

static void callchain_debug(void)
{
- static const char *str[CALLCHAIN_MAX] = { "NONE", "FP", "DWARF" };
+ static const char *str[CALLCHAIN_MAX] = { "NONE", "FP", "DWARF", "LBR" };

pr_debug("callchain: type %s\n", str[callchain_param.record_mode]);

@@ -751,9 +751,9 @@ static struct record record = {
#define CALLCHAIN_HELP "setup and enables call-graph (stack chain/backtrace) recording: "

#ifdef HAVE_DWARF_UNWIND_SUPPORT
-const char record_callchain_help[] = CALLCHAIN_HELP "fp dwarf";
+const char record_callchain_help[] = CALLCHAIN_HELP "fp dwarf lbr";
#else
-const char record_callchain_help[] = CALLCHAIN_HELP "fp";
+const char record_callchain_help[] = CALLCHAIN_HELP "fp lbr";
#endif

/*
diff --git a/tools/perf/builtin-report.c b/tools/perf/builtin-report.c
index 2f91094..0ba5f07 100644
--- a/tools/perf/builtin-report.c
+++ b/tools/perf/builtin-report.c
@@ -249,6 +249,8 @@ static int report__setup_sample_type(struct report *rep)
if ((sample_type & PERF_SAMPLE_REGS_USER) &&
(sample_type & PERF_SAMPLE_STACK_USER))
callchain_param.record_mode = CALLCHAIN_DWARF;
+ else if (sample_type & PERF_SAMPLE_BRANCH_STACK)
+ callchain_param.record_mode = CALLCHAIN_LBR;
else
callchain_param.record_mode = CALLCHAIN_FP;
}
diff --git a/tools/perf/util/callchain.c b/tools/perf/util/callchain.c
index 14e7a12..9f643ee 100644
--- a/tools/perf/util/callchain.c
+++ b/tools/perf/util/callchain.c
@@ -97,6 +97,14 @@ int parse_callchain_record_opt(const char *arg)
callchain_param.dump_size = size;
}
#endif /* HAVE_DWARF_UNWIND_SUPPORT */
+ } else if (!strncmp(name, "lbr", sizeof("lbr"))) {
+ if (!strtok_r(NULL, ",", &saveptr)) {
+ callchain_param.record_mode = CALLCHAIN_LBR;
+ ret = 0;
+ } else
+ pr_err("callchain: No more arguments "
+ "needed for --call-graph lbr\n");
+ break;
} else {
pr_err("callchain: Unknown --call-graph option "
"value: %s\n", arg);
diff --git a/tools/perf/util/callchain.h b/tools/perf/util/callchain.h
index c0ec1ac..6033a0a 100644
--- a/tools/perf/util/callchain.h
+++ b/tools/perf/util/callchain.h
@@ -11,6 +11,7 @@ enum perf_call_graph_mode {
CALLCHAIN_NONE,
CALLCHAIN_FP,
CALLCHAIN_DWARF,
+ CALLCHAIN_LBR,
CALLCHAIN_MAX
};

diff --git a/tools/perf/util/evsel.c b/tools/perf/util/evsel.c
index ea51a90..f93e520 100644
--- a/tools/perf/util/evsel.c
+++ b/tools/perf/util/evsel.c
@@ -537,13 +537,30 @@ int perf_evsel__group_desc(struct perf_evsel *evsel, char *buf, size_t size)
}

static void
-perf_evsel__config_callgraph(struct perf_evsel *evsel)
+perf_evsel__config_callgraph(struct perf_evsel *evsel,
+ struct record_opts *opts)
{
bool function = perf_evsel__is_function_event(evsel);
struct perf_event_attr *attr = &evsel->attr;

perf_evsel__set_sample_bit(evsel, CALLCHAIN);

+ if (callchain_param.record_mode == CALLCHAIN_LBR) {
+ if (!opts->branch_stack) {
+ if (attr->exclude_user) {
+ pr_warning("LBR callstack option is only available "
+ "to get user callchain information. "
+ "Falling back to framepointers.\n");
+ } else {
+ perf_evsel__set_sample_bit(evsel, BRANCH_STACK);
+ attr->branch_sample_type = PERF_SAMPLE_BRANCH_USER |
+ PERF_SAMPLE_BRANCH_CALL_STACK;
+ }
+ } else
+ pr_warning("Cannot use LBR callstack with branch stack. "
+ "Falling back to framepointers.\n");
+ }
+
if (callchain_param.record_mode == CALLCHAIN_DWARF) {
if (!function) {
perf_evsel__set_sample_bit(evsel, REGS_USER);
@@ -667,7 +684,7 @@ void perf_evsel__config(struct perf_evsel *evsel, struct record_opts *opts)
evsel->attr.exclude_callchain_user = 1;

if (callchain_param.enabled && !evsel->no_aux_samples)
- perf_evsel__config_callgraph(evsel);
+ perf_evsel__config_callgraph(evsel, opts);

if (opts->sample_intr_regs) {
attr->sample_regs_intr = PERF_REGS_MASK;
--
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Next message: tip-bot for Kan Liang: "[tip:perf/core] perf tools: Construct LBR call chain"
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