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@kernel.org>
Signed-off-by: Kan Liang <kan.liang@intel.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: Anshuman Khandual <khandual@linux.vnet.ibm.com>
Cc: Arnaldo Carvalho de Melo <acme@kernel.org>
Cc: Cody P Schafer <cody@linux.vnet.ibm.com>
Cc: David Ahern <dsahern@gmail.com>
Cc: Don Zickus <dzickus@redhat.com>
Cc: Jacob Shin <jacob.w.shin@gmail.com>
Cc: Jiri Olsa <jolsa@redhat.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Masanari Iida <standby24x7@gmail.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Rodrigo Campos <rodrigo@sdfg.com.ar>
Cc: Stephane Eranian <eranian@google.com>
Cc: Sukadev Bhattiprolu <sukadev@linux.vnet.ibm.com>
Link: http://lkml.kernel.org/r/1420482185-29830-2-git-send-email-kan.liang@intel.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>

6 files changed, 40 insertions, 6 deletions

diff --git a/tools/perf/Documentation/perf-record.txt b/tools/perf/Documentation/perf-record.txt
index 31e977459c51..1c7e50f62b1f 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 404ab3434052..d0d02a811ecd 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 2f91094e228b..0ba5f07906fb 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 14e7a123d43b..9f643ee77001 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 c0ec1acc38e4..6033a0a212ca 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 ea51a90e20a0..f93e5208c762 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;