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

[Arnaldo Carvalho de Melo]

Em Mon, Mar 13, 2023 at 01:48:21PM -0700, Namhyung Kim escreveu:
> 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.

Beautiful :-)

And the csets are _so_ small and demonstrate techniques that should be
used in more and more tools.

Applied, testing.

- Arnaldo
 
> 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
> -- 
> 2.40.0.rc1.284.g88254d51c5-goog
> 

-- 

- Arnaldo