[PATCH 7/7] perf lock: Look up callchain for the contended locks

[Namhyung Kim]

The lock contention tracepoints don't provide lock names.  All we can
do is to get stack traces and show the caller instead.  To minimize
the overhead it's limited to up to 8 stack traces and display the
first non-lock function symbol name as a caller.

  $ perf lock report -F acquired,contended,avg_wait,wait_total

                  Name   acquired  contended     avg wait    total wait

   update_blocked_a...         40         40      3.61 us     144.45 us
   kernfs_fop_open+...          5          5      3.64 us      18.18 us
    _nohz_idle_balance          3          3      2.65 us       7.95 us
   tick_do_update_j...          1          1      6.04 us       6.04 us
    ep_scan_ready_list          1          1      3.93 us       3.93 us
  ...

Acked-by: Ian Rogers <irogers@xxxxxxxxxx>
Signed-off-by: Namhyung Kim <namhyung@xxxxxxxxxx>
---
 tools/perf/builtin-lock.c | 172 +++++++++++++++++++++++++++++++++++++-
 1 file changed, 168 insertions(+), 4 deletions(-)

diff --git a/tools/perf/builtin-lock.c b/tools/perf/builtin-lock.c
index a677ad9507c3..93e958a7f844 100644
--- a/tools/perf/builtin-lock.c
+++ b/tools/perf/builtin-lock.c
@@ -9,6 +9,7 @@
 #include "util/symbol.h"
 #include "util/thread.h"
 #include "util/header.h"
+#include "util/callchain.h"
 
 #include <subcmd/pager.h>
 #include <subcmd/parse-options.h>
@@ -19,6 +20,7 @@
 #include "util/tool.h"
 #include "util/data.h"
 #include "util/string2.h"
+#include "util/map.h"
 
 #include <sys/types.h>
 #include <sys/prctl.h>
@@ -32,6 +34,7 @@
 #include <linux/kernel.h>
 #include <linux/zalloc.h>
 #include <linux/err.h>
+#include <linux/stringify.h>
 
 static struct perf_session *session;
 
@@ -120,6 +123,24 @@ static struct rb_root		thread_stats;
 static bool combine_locks;
 static bool show_thread_stats;
 
+/*
+ * CONTENTION_STACK_DEPTH
+ * Number of stack trace entries to find callers
+ */
+#define CONTENTION_STACK_DEPTH  8
+
+/*
+ * CONTENTION_STACK_SKIP
+ * Number of stack trace entries to skip when finding callers.
+ * The first few entries belong to the locking implementation itself.
+ */
+#define CONTENTION_STACK_SKIP  3
+
+static u64 sched_text_start;
+static u64 sched_text_end;
+static u64 lock_text_start;
+static u64 lock_text_end;
+
 static struct thread_stat *thread_stat_find(u32 tid)
 {
 	struct rb_node *node;
@@ -483,6 +504,18 @@ static struct lock_stat *pop_from_result(void)
 	return container_of(node, struct lock_stat, rb);
 }
 
+static struct lock_stat *lock_stat_find(u64 addr)
+{
+	struct hlist_head *entry = lockhashentry(addr);
+	struct lock_stat *ret;
+
+	hlist_for_each_entry(ret, entry, hash_entry) {
+		if (ret->addr == addr)
+			return ret;
+	}
+	return NULL;
+}
+
 static struct lock_stat *lock_stat_findnew(u64 addr, const char *name)
 {
 	struct hlist_head *entry = lockhashentry(addr);
@@ -825,6 +858,116 @@ static int report_lock_release_event(struct evsel *evsel,
 	return 0;
 }
 
+static bool is_lock_function(u64 addr)
+{
+	if (!sched_text_start) {
+		struct machine *machine = &session->machines.host;
+		struct map *kmap;
+		struct symbol *sym;
+
+		sym = machine__find_kernel_symbol_by_name(machine,
+							  "__sched_text_start",
+							  &kmap);
+		if (!sym) {
+			/* to avoid retry */
+			sched_text_start = 1;
+			return false;
+		}
+
+		sched_text_start = kmap->unmap_ip(kmap, sym->start);
+
+		/* should not fail from here */
+		sym = machine__find_kernel_symbol_by_name(machine,
+							  "__sched_text_end",
+							  &kmap);
+		sched_text_end = kmap->unmap_ip(kmap, sym->start);
+
+		sym = machine__find_kernel_symbol_by_name(machine,
+							  "__lock_text_start",
+							  &kmap);
+		lock_text_start = kmap->unmap_ip(kmap, sym->start);
+
+		sym = machine__find_kernel_symbol_by_name(machine,
+							  "__lock_text_end",
+							  &kmap);
+		lock_text_start = kmap->unmap_ip(kmap, sym->start);
+	}
+
+	/* failed to get kernel symbols */
+	if (sched_text_start == 1)
+		return false;
+
+	/* mutex and rwsem functions are in sched text section */
+	if (sched_text_start <= addr && addr < sched_text_end)
+		return true;
+
+	/* spinlock functions are in lock text section */
+	if (lock_text_start <= addr && addr < lock_text_end)
+		return true;
+
+	return false;
+}
+
+static int lock_contention_caller(struct evsel *evsel, struct perf_sample *sample,
+				  char *buf, int size)
+{
+	struct thread *thread;
+	struct callchain_cursor *cursor = &callchain_cursor;
+	struct symbol *sym;
+	int skip = 0;
+	int ret;
+
+	/* lock names will be replaced to task name later */
+	if (show_thread_stats)
+		return -1;
+
+	thread = machine__findnew_thread(&session->machines.host,
+					 -1, sample->pid);
+	if (thread == NULL)
+		return -1;
+
+	/* use caller function name from the callchain */
+	ret = thread__resolve_callchain(thread, cursor, evsel, sample,
+					NULL, NULL, CONTENTION_STACK_DEPTH);
+	if (ret != 0) {
+		thread__put(thread);
+		return -1;
+	}
+
+	callchain_cursor_commit(cursor);
+	thread__put(thread);
+
+	while (true) {
+		struct callchain_cursor_node *node;
+
+		node = callchain_cursor_current(cursor);
+		if (node == NULL)
+			break;
+
+		/* skip first few entries - for lock functions */
+		if (++skip <= CONTENTION_STACK_SKIP)
+			goto next;
+
+		sym = node->ms.sym;
+		if (sym && !is_lock_function(node->ip)) {
+			struct map *map = node->ms.map;
+			u64 offset;
+
+			offset = map->map_ip(map, node->ip) - sym->start;
+
+			if (offset)
+				scnprintf(buf, size, "%s+%#lx", sym->name, offset);
+			else
+				strlcpy(buf, sym->name, size);
+			return 0;
+		}
+
+next:
+		callchain_cursor_advance(cursor);
+	}
+	return -1;
+}
+
 static int report_lock_contention_begin_event(struct evsel *evsel,
 					      struct perf_sample *sample)
 {
@@ -836,9 +979,18 @@ static int report_lock_contention_begin_event(struct evsel *evsel,
 	if (show_thread_stats)
 		addr = sample->tid;
 
-	ls = lock_stat_findnew(addr, "No name");
-	if (!ls)
-		return -ENOMEM;
+	ls = lock_stat_find(addr);
+	if (!ls) {
+		char buf[128];
+		const char *caller = buf;
+
+		if (lock_contention_caller(evsel, sample, buf, sizeof(buf)) < 0)
+			caller = "Unknown";
+
+		ls = lock_stat_findnew(addr, caller);
+		if (!ls)
+			return -ENOMEM;
+	}
 
 	ts = thread_stat_findnew(sample->tid);
 	if (!ts)
@@ -1219,6 +1371,7 @@ static int __cmd_report(bool display_info)
 	struct perf_tool eops = {
 		.sample		 = process_sample_event,
 		.comm		 = perf_event__process_comm,
+		.mmap		 = perf_event__process_mmap,
 		.namespaces	 = perf_event__process_namespaces,
 		.ordered_events	 = true,
 	};
@@ -1234,6 +1387,8 @@ static int __cmd_report(bool display_info)
 		return PTR_ERR(session);
 	}
 
+	/* for lock function check */
+	symbol_conf.sort_by_name = true;
 	symbol__init(&session->header.env);
 
 	if (!perf_session__has_traces(session, "lock record"))
@@ -1278,8 +1433,12 @@ static int __cmd_record(int argc, const char **argv)
 	const char *record_args[] = {
 		"record", "-R", "-m", "1024", "-c", "1", "--synth", "task",
 	};
+	const char *callgraph_args[] = {
+		"--call-graph", "fp," __stringify(CONTENTION_STACK_DEPTH),
+	};
 	unsigned int rec_argc, i, j, ret;
 	unsigned int nr_tracepoints;
+	unsigned int nr_callgraph_args = 0;
 	const char **rec_argv;
 	bool has_lock_stat = true;
 
@@ -1304,8 +1463,10 @@ static int __cmd_record(int argc, const char **argv)
 		}
 	}
 
+	nr_callgraph_args = ARRAY_SIZE(callgraph_args);
+
 setup_args:
-	rec_argc = ARRAY_SIZE(record_args) + argc - 1;
+	rec_argc = ARRAY_SIZE(record_args) + nr_callgraph_args + argc - 1;
 
 	if (has_lock_stat)
 		nr_tracepoints = ARRAY_SIZE(lock_tracepoints);
@@ -1337,6 +1498,9 @@ static int __cmd_record(int argc, const char **argv)
 		rec_argv[i++] = ev_name;
 	}
 
+	for (j = 0; j < nr_callgraph_args; j++, i++)
+		rec_argv[i] = callgraph_args[j];
+
 	for (j = 1; j < (unsigned int)argc; j++, i++)
 		rec_argv[i] = argv[j];
 
-- 
2.36.1.255.ge46751e96f-goog