[PATCH 0/4] perf lock contention: Improve lock symbol display (v1)

Namhyung Kim
2023-03-13T20:48:35Z

Hello,

This patchset improves the symbolization of locks for -l/--lock-addr mode.
As of now it only shows global lock symbols present in the kallsyms. But
we can add some more lock symbols by traversing pointers in the BPF program.

For example, mmap_lock can be reached from the mm_struct of the current task
(task_struct->mm->mmap_lock) and we can compare the address of the give lock
with it. Similarly I've added 'siglock' for current->sighand->siglock.

On the other hand, we can traverse some of semi-global locks like per-cpu,
per-device, per-filesystem and so on. I've added 'rqlock' for each cpu's
runqueue lock.

It cannot cover all types of locks in the system but it'd be fairly usefule
if we can add many of often contended locks. I tried to add futex locks
but it failed to find the __futex_data symbol from BTF. I'm not sure why but
I guess it's because the struct doesn't have a tag name.

Those locks are added just because they got caught during my test.
It'd be nice if you suggest which locks to add and how to do that. :)
I'm thinking if there's a way to track file-based locks (like epoll, etc).

Finally I also added a lock type name after the symbols (if any) so that we
can get some idea even though it has no symbol. The example output looks
like below:

$ sudo ./perf lock con -abl -- sleep 1
contended total wait max wait avg wait address symbol

44 6.13 ms 284.49 us 139.28 us ffffffff92e06080 tasklist_lock (rwlock)
159 983.38 us 12.38 us 6.18 us ffff8cc717c90000 siglock (spinlock)
10 679.90 us 153.35 us 67.99 us ffff8cdc2872aaf8 mmap_lock (rwsem)
9 558.11 us 180.67 us 62.01 us ffff8cd647914038 mmap_lock (rwsem)
78 228.56 us 7.82 us 2.93 us ffff8cc700061c00 (spinlock)
5 41.60 us 16.93 us 8.32 us ffffd853acb41468 (spinlock)
10 37.24 us 5.87 us 3.72 us ffff8cd560b5c200 siglock (spinlock)
4 11.17 us 3.97 us 2.79 us ffff8d053ddf0c80 rq_lock (spinlock)
1 7.86 us 7.86 us 7.86 us ffff8cd64791404c (spinlock)
1 4.13 us 4.13 us 4.13 us ffff8d053d930c80 rq_lock (spinlock)
7 3.98 us 1.67 us 568 ns ffff8ccb92479440 (mutex)
2 2.62 us 2.33 us 1.31 us ffff8cc702e6ede0 (rwlock)

The tasklist_lock is global so it's from the kallsyms. But others like
siglock, mmap_lock and rq_lock are from the BPF.

You get get the code at 'perf/lock-symbol-v1' branch in

git://git.kernel.org/pub/scm/linux/kernel/git/namhyung/linux-perf.git

Thanks,
Namhyung

Namhyung Kim (4):
perf lock contention: Track and show mmap_lock with address
perf lock contention: Track and show siglock with address
perf lock contention: Show per-cpu rq_lock with address
perf lock contention: Show lock type with address

tools/perf/builtin-lock.c | 46 +++++++----
tools/perf/util/bpf_lock_contention.c | 35 ++++++++-
.../perf/util/bpf_skel/lock_contention.bpf.c | 77 +++++++++++++++++++
tools/perf/util/bpf_skel/lock_data.h | 14 ++++
4 files changed, 152 insertions(+), 20 deletions(-)

base-commit: b8fa3e3833c14151a47ebebbc5427dcfe94bb407
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2.40.0.rc1.284.g88254d51c5-goog