[PATCH 1/4] perf lock contention: Track and show mmap_lock with address

Namhyung Kim
2023-03-13T20:48:41Z

Sometimes there are severe contentions on the mmap_lock and we want
see it in the -l/--lock-addr output. However it cannot symbolize
the mmap_lock because it's allocated dynamically without symbols.

Stephane and Hao gave me an idea separately to display mmap_lock by
following the current->mm pointer. I added a flag to mark mmap_lock
after comparing the lock address so that it can show them differently.
With this change it can show mmap_lock like below:

$ sudo ./perf lock con -abl -- sleep 10
contended total wait max wait avg wait address symbol
...
16344 312.30 ms 2.22 ms 19.11 us ffff8cc702595640
17686 310.08 ms 1.49 ms 17.53 us ffff8cc7025952c0
3 84.14 ms 45.79 ms 28.05 ms ffff8cc78114c478 mmap_lock
3557 76.80 ms 68.75 us 21.59 us ffff8cc77ca3af58
1 68.27 ms 68.27 ms 68.27 ms ffff8cda745dfd70
9 54.53 ms 7.96 ms 6.06 ms ffff8cc7642a48b8 mmap_lock
14629 44.01 ms 60.00 us 3.01 us ffff8cc7625f9ca0
3481 42.63 ms 140.71 us 12.24 us ffffffff937906ac vmap_area_lock
16194 38.73 ms 42.15 us 2.39 us ffff8cd397cbc560
11 38.44 ms 10.39 ms 3.49 ms ffff8ccd6d12fbb8 mmap_lock
1 5.43 ms 5.43 ms 5.43 ms ffff8cd70018f0d8
1674 5.38 ms 422.93 us 3.21 us ffffffff92e06080 tasklist_lock
581 4.51 ms 130.68 us 7.75 us ffff8cc9b1259058
5 3.52 ms 1.27 ms 703.23 us ffff8cc754510070
112 3.47 ms 56.47 us 31.02 us ffff8ccee38b3120
381 3.31 ms 73.44 us 8.69 us ffffffff93790690 purge_vmap_area_lock
255 3.19 ms 36.35 us 12.49 us ffff8d053ce30c80

Note that mmap_lock was renamed some time ago and it needs to support
old kernels with a different name 'mmap_sem'.

Suggested-by: Stephane Eranian <eranian@google.com>
Suggested-by: Hao Luo <haoluo@google.com>
Cc: Suren Baghdasaryan <surenb@google.com>
Signed-off-by: Namhyung Kim <namhyung@kernel.org>
---
tools/perf/builtin-lock.c | 2 +-
.../perf/util/bpf_skel/lock_contention.bpf.c | 41 +++++++++++++++++++
tools/perf/util/bpf_skel/lock_data.h | 6 +++
3 files changed, 48 insertions(+), 1 deletion(-)

diff --git a/tools/perf/builtin-lock.c b/tools/perf/builtin-lock.c
index 054997edd98b..c62f4d9363a6 100644
--- a/tools/perf/builtin-lock.c
+++ b/tools/perf/builtin-lock.c
@@ -1663,7 +1663,7 @@ static void print_contention_result(struct lock_contention *con)
break;
case LOCK_AGGR_ADDR:
pr_info(" %016llx %s\n", (unsigned long long)st->addr,
- st->name ? : "");
+ (st->flags & LCD_F_MMAP_LOCK) ? "mmap_lock" : st->name);
break;
default:
break;
diff --git a/tools/perf/util/bpf_skel/lock_contention.bpf.c b/tools/perf/util/bpf_skel/lock_contention.bpf.c
index e6007eaeda1a..f092a78ae2b5 100644
--- a/tools/perf/util/bpf_skel/lock_contention.bpf.c
+++ b/tools/perf/util/bpf_skel/lock_contention.bpf.c
@@ -92,6 +92,14 @@ struct rw_semaphore___new {
atomic_long_t owner;
} __attribute__((preserve_access_index));

+struct mm_struct___old {
+ struct rw_semaphore mmap_sem;
+} __attribute__((preserve_access_index));
+
+struct mm_struct___new {
+ struct rw_semaphore mmap_lock;
+} __attribute__((preserve_access_index));
+
/* control flags */
int enabled;
int has_cpu;
@@ -204,6 +212,36 @@ static inline struct task_struct *get_lock_owner(__u64 lock, __u32 flags)
return task;
}

+static inline __u32 check_lock_type(__u64 lock, __u32 flags)
+{
+ struct task_struct *curr;
+ struct mm_struct___old *mm_old;
+ struct mm_struct___new *mm_new;
+
+ switch (flags) {
+ case LCB_F_READ: /* rwsem */
+ case LCB_F_WRITE:
+ curr = bpf_get_current_task_btf();
+ if (curr->mm == NULL)
+ break;
+ mm_new = (void *)curr->mm;
+ if (bpf_core_field_exists(mm_new->mmap_lock)) {
+ if (&mm_new->mmap_lock == (void *)lock)
+ return LCD_F_MMAP_LOCK;
+ break;
+ }
+ mm_old = (void *)curr->mm;
+ if (bpf_core_field_exists(mm_old->mmap_sem)) {
+ if (&mm_old->mmap_sem == (void *)lock)
+ return LCD_F_MMAP_LOCK;
+ }
+ break;
+ default:
+ break;
+ }
+ return 0;
+}
+
SEC("tp_btf/contention_begin")
int contention_begin(u64 *ctx)
{
@@ -314,6 +352,9 @@ int contention_end(u64 *ctx)
.flags = pelem->flags,
};

+ if (aggr_mode == LOCK_AGGR_ADDR)
+ first.flags |= check_lock_type(pelem->lock, pelem->flags);
+
bpf_map_update_elem(&lock_stat, &key, &first, BPF_NOEXIST);
bpf_map_delete_elem(&tstamp, &pid);
return 0;
diff --git a/tools/perf/util/bpf_skel/lock_data.h b/tools/perf/util/bpf_skel/lock_data.h
index 3d35fd4407ac..789f20833798 100644
--- a/tools/perf/util/bpf_skel/lock_data.h
+++ b/tools/perf/util/bpf_skel/lock_data.h
@@ -15,6 +15,12 @@ struct contention_task_data {
char comm[TASK_COMM_LEN];
};

+/*
+ * Upper bits of the flags in the contention_data are used to identify
+ * some well-known locks which do not have symbols (non-global locks).
+ */
+#define LCD_F_MMAP_LOCK (1U << 31)
+
struct contention_data {
u64 total_time;
u64 min_time;
--
2.40.0.rc1.284.g88254d51c5-goog