[PATCH v1] perf lock contention: skip traceiter functions

Anne Macedo
2024-03-09T13:27:26Z

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 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 | 17 +++++++++++++++++
tools/perf/util/machine.h | 2 +-
2 files changed, 18 insertions(+), 1 deletion(-)

diff --git a/tools/perf/util/machine.c b/tools/perf/util/machine.c
index 527517db3182..db443947ccd1 100644
--- a/tools/perf/util/machine.c
+++ b/tools/perf/util/machine.c
@@ -3266,6 +3266,14 @@ 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);
+ machine->traceiter.text_start = map__unmap_ip(kmap, sym->start);
+ machine->traceiter.text_end = map__unmap_ip(kmap, sym->end);
+
+ sym = machine__find_kernel_symbol_by_name(machine, "trace_contention_begin", &kmap);
+ machine->trace.text_start = map__unmap_ip(kmap, sym->start);
+ machine->trace.text_end = map__unmap_ip(kmap, sym->end);
}

/* failed to get kernel symbols */
@@ -3280,5 +3288,14 @@ 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 <= addr && addr < machine->traceiter.text_end)
+ return true;
+
+ 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