[PATCH v2 2/8] perf tools: Support printing callchains with arrows

[Namhyung Kim <namhyung@kernel.org>]

The EVSEL__PRINT_CALLCHAIN_ARROW options can be used to print callchains
with arrows for readability.  It will be used 'sched timehist' command
like below:

    __schedule <- schedule <- schedule_timeout <- rcu_gp_kthread <- kthread <- ret_from_fork
    __schedule <- schedule <- schedule_timeout <- rcu_gp_kthread <- kthread <- ret_from_fork
    __schedule <- schedule <- worker_thread <- kthread <- ret_from_fork

Suggested-by: Ingo Molnar <mingo@kernel.org>
Signed-off-by: Namhyung Kim <namhyung@kernel.org>
---
 tools/perf/util/evsel.h         | 1 +
 tools/perf/util/evsel_fprintf.c | 6 ++++++
 2 files changed, 7 insertions(+)

diff --git a/tools/perf/util/evsel.h b/tools/perf/util/evsel.h
index 8cd7cd227483..27fa3a343577 100644
--- a/tools/perf/util/evsel.h
+++ b/tools/perf/util/evsel.h
@@ -391,6 +391,7 @@ int perf_evsel__fprintf(struct perf_evsel *evsel,
 #define EVSEL__PRINT_ONELINE		(1<<4)
 #define EVSEL__PRINT_SRCLINE		(1<<5)
 #define EVSEL__PRINT_UNKNOWN_AS_ADDR	(1<<6)
+#define EVSEL__PRINT_CALLCHAIN_ARROW	(1<<7)
 
 struct callchain_cursor;
 
diff --git a/tools/perf/util/evsel_fprintf.c b/tools/perf/util/evsel_fprintf.c
index ccb602397b60..53bb614feafb 100644
--- a/tools/perf/util/evsel_fprintf.c
+++ b/tools/perf/util/evsel_fprintf.c
@@ -108,7 +108,9 @@ int sample__fprintf_callchain(struct perf_sample *sample, int left_alignment,
 	int print_oneline = print_opts & EVSEL__PRINT_ONELINE;
 	int print_srcline = print_opts & EVSEL__PRINT_SRCLINE;
 	int print_unknown_as_addr = print_opts & EVSEL__PRINT_UNKNOWN_AS_ADDR;
+	int print_arrow = print_opts & EVSEL__PRINT_CALLCHAIN_ARROW;
 	char s = print_oneline ? ' ' : '\t';
+	bool first = true;
 
 	if (sample->callchain) {
 		struct addr_location node_al;
@@ -124,6 +126,9 @@ int sample__fprintf_callchain(struct perf_sample *sample, int left_alignment,
 
 			printed += fprintf(fp, "%-*.*s", left_alignment, left_alignment, " ");
 
+			if (print_arrow && !first)
+				printed += fprintf(fp, " <-");
+
 			if (print_ip)
 				printed += fprintf(fp, "%c%16" PRIx64, s, node->ip);
 
@@ -158,6 +163,7 @@ int sample__fprintf_callchain(struct perf_sample *sample, int left_alignment,
 				printed += fprintf(fp, "\n");
 
 			callchain_cursor_advance(cursor);
+			first = false;
 		}
 	}
 
-- 
2.10.1