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From: Anne Macedo <retpolanne@posteo.net>
To: Arnaldo Carvalho de Melo <acme@kernel.org>,
	Namhyung Kim <namhyung@kernel.org>
Cc: Anne Macedo <retpolanne@posteo.net>,
	Peter Zijlstra <peterz@infradead.org>,
	Ingo Molnar <mingo@redhat.com>,
	Mark Rutland <mark.rutland@arm.com>,
	Alexander Shishkin <alexander.shishkin@linux.intel.com>,
	Jiri Olsa <jolsa@kernel.org>,
	Ian Rogers <irogers@google.com>,
	Adrian Hunter <adrian.hunter@intel.com>,
	linux-perf-users@vger.kernel.org,
	linux-kernel@vger.kernel.org
Subject: [PATCH v3] perf lock contention: skip traceiter functions
Date: Fri, 15 Mar 2024 11:19:05 +0000
Message-Id: <20240315111907.1434909-1-retpolanne@posteo.net>
Precedence: bulk
MIME-Version: 1.0
Content-Transfer-Encoding: 8bit

The perf lock contention program currently shows the caller of the locks
as __traceiter_contention_begin+0x??. This caller can be ignored, as it is
from the traceiter itself. Instead, it should show the real callers for
the locks.

When fiddling with the --stack-skip parameter, the actual callers for
the locks start to show up. However, just ignore the
__traceiter_contention_begin and the __traceiter_contention_end symbols
so the actual callers will show up.

Before this patch is applied:

sudo perf lock con -a -b -- sleep 3
 contended   total wait     max wait     avg wait         type   caller

         8      2.33 s       2.28 s     291.18 ms     rwlock:W   __traceiter_contention_begin+0x44
         4      2.33 s       2.28 s     582.35 ms     rwlock:W   __traceiter_contention_begin+0x44
         7    140.30 ms     46.77 ms     20.04 ms     rwlock:W   __traceiter_contention_begin+0x44
         2     63.35 ms     33.76 ms     31.68 ms        mutex   trace_contention_begin+0x84
         2     46.74 ms     46.73 ms     23.37 ms     rwlock:W   __traceiter_contention_begin+0x44
         1     13.54 us     13.54 us     13.54 us        mutex   trace_contention_begin+0x84
         1      3.67 us      3.67 us      3.67 us      rwsem:R   __traceiter_contention_begin+0x44

Before this patch is applied - using --stack-skip 5

sudo perf lock con --stack-skip 5 -a -b -- sleep 3
 contended   total wait     max wait     avg wait         type   caller

         2      2.24 s       2.24 s       1.12 s      rwlock:W   do_epoll_wait+0x5a0
         4      1.65 s     824.21 ms    412.08 ms     rwlock:W   do_exit+0x338
         2    824.35 ms    824.29 ms    412.17 ms     spinlock   get_signal+0x108
         2    824.14 ms    824.14 ms    412.07 ms     rwlock:W   release_task+0x68
         1     25.22 ms     25.22 ms     25.22 ms        mutex   cgroup_kn_lock_live+0x58
         1     24.71 us     24.71 us     24.71 us     spinlock   do_exit+0x44
         1     22.04 us     22.04 us     22.04 us      rwsem:R   lock_mm_and_find_vma+0xb0

After this patch is applied:

sudo ./perf lock con -a -b -- sleep 3
 contended   total wait     max wait     avg wait         type   caller

         4      4.13 s       2.07 s       1.03 s      rwlock:W   release_task+0x68
         2      2.07 s       2.07 s       1.03 s      rwlock:R   mm_update_next_owner+0x50
         2      2.07 s       2.07 s       1.03 s      rwlock:W   do_exit+0x338
         1     41.56 ms     41.56 ms     41.56 ms        mutex   cgroup_kn_lock_live+0x58
         2     36.12 us     18.83 us     18.06 us     rwlock:W   do_exit+0x338

changes since v2:

- add dummy value to machine->traceiter and machine->trace to make
necessary checks, fixing possible null pointer access

changes since v1:

- consider trace_contention and __traceiter_contention functions as
optional (i.e. check if sym is null to avoid segfault)

changes since v0:

- skip trace_contention functions
- use sym->end instead of __traceiter_contention_end for text_end

Signed-off-by: Anne Macedo <retpolanne@posteo.net>
---
 tools/perf/util/machine.c | 29 +++++++++++++++++++++++++++++
 tools/perf/util/machine.h |  2 +-
 2 files changed, 30 insertions(+), 1 deletion(-)

diff --git a/tools/perf/util/machine.c b/tools/perf/util/machine.c
index 527517db3182..373a3b852f72 100644
--- a/tools/perf/util/machine.c
+++ b/tools/perf/util/machine.c
@@ -3266,6 +3266,22 @@ bool machine__is_lock_function(struct machine *machine, u64 addr)
 
 		sym = machine__find_kernel_symbol_by_name(machine, "__lock_text_end", &kmap);
 		machine->lock.text_end = map__unmap_ip(kmap, sym->start);
+
+		sym = machine__find_kernel_symbol_by_name(machine, "__traceiter_contention_begin", &kmap);
+		if (sym) {
+			machine->traceiter.text_start = map__unmap_ip(kmap, sym->start);
+			machine->traceiter.text_end = map__unmap_ip(kmap, sym->end);
+		} else {
+			machine->traceiter.text_start = 1;
+		}
+
+		sym = machine__find_kernel_symbol_by_name(machine, "trace_contention_begin", &kmap);
+		if (sym) {
+			machine->trace.text_start = map__unmap_ip(kmap, sym->start);
+			machine->trace.text_end = map__unmap_ip(kmap, sym->end);
+		} else {
+			machine->trace.text_start = 1;
+		}
 	}
 
 	/* failed to get kernel symbols */
@@ -3280,5 +3296,18 @@ bool machine__is_lock_function(struct machine *machine, u64 addr)
 	if (machine->lock.text_start <= addr && addr < machine->lock.text_end)
 		return true;
 
+	/* traceiter functions currently don't have their own section
+	 * but we consider them lock functions
+	 */
+	if (machine->traceiter.text_start != 1) {
+		if (machine->traceiter.text_start <= addr && addr < machine->traceiter.text_end)
+			return true;
+	}
+
+	if (machine->trace.text_start != 1) {
+		if (machine->trace.text_start <= addr && addr < machine->trace.text_end)
+			return true;
+	}
+
 	return false;
 }
diff --git a/tools/perf/util/machine.h b/tools/perf/util/machine.h
index e28c787616fe..4312f6db6de0 100644
--- a/tools/perf/util/machine.h
+++ b/tools/perf/util/machine.h
@@ -49,7 +49,7 @@ struct machine {
 	struct {
 		u64	  text_start;
 		u64	  text_end;
-	} sched, lock;
+	} sched, lock, traceiter, trace;
 	pid_t		  *current_tid;
 	size_t		  current_tid_sz;
 	union { /* Tool specific area */
-- 
2.39.2