Re: [PATCH v3 0/4] perf lock contention: Symbolize locks using slab cache names

[Arnaldo Carvalho de Melo <acme@kernel.org>]

On Thu, Dec 19, 2024 at 10:00:05PM -0800, Namhyung Kim wrote:
> Hello,
> 
> This is to support symbolization of dynamic locks using slab
> allocator's metadata.  The kernel support is merged to v6.13.
> 
> It provides the new "kmem_cache" BPF iterator and "bpf_get_kmem_cache"
> kfunc to get the information from an address.  The feature detection is
> done using BTF type info and it won't have any effect on old kernels.
> 
> v3 changes)
> 
>  * fix build error with GEN_VMLINUX_H=1  (Arnaldo)

Thanks, applied to perf-tools-next,

- Arnaldo

>  * update comment to explain slab cache ID  (Vlastimil)
>  * add Ian's Acked-by
> 
> v2) https://lore.kernel.org/linux-perf-users/20241108061500.2698340-1-namhyung@kernel.org
> 
>  * don't use libbpf_get_error()  (Andrii)
> 
> v1) https://lore.kernel.org/linux-perf-users/20241105172635.2463800-1-namhyung@kernel.org
> 
> With this change, it can show locks in a slab object like below.  I
> added "&" sign to distinguish them from global locks.
> 
>     # perf lock con -abl sleep 1
>      contended   total wait     max wait     avg wait            address   symbol
> 
>              2      1.95 us      1.77 us       975 ns   ffff9d5e852d3498   &task_struct (mutex)
>              1      1.18 us      1.18 us      1.18 us   ffff9d5e852d3538   &task_struct (mutex)
>              4      1.12 us       354 ns       279 ns   ffff9d5e841ca800   &kmalloc-cg-512 (mutex)
>              2       859 ns       617 ns       429 ns   ffffffffa41c3620   delayed_uprobe_lock (mutex)
>              3       691 ns       388 ns       230 ns   ffffffffa41c0940   pack_mutex (mutex)
>              3       421 ns       164 ns       140 ns   ffffffffa3a8b3a0   text_mutex (mutex)
>              1       409 ns       409 ns       409 ns   ffffffffa41b4cf8   tracepoint_srcu_srcu_usage (mutex)
>              2       362 ns       239 ns       181 ns   ffffffffa41cf840   pcpu_alloc_mutex (mutex)
>              1       220 ns       220 ns       220 ns   ffff9d5e82b534d8   &signal_cache (mutex)
>              1       215 ns       215 ns       215 ns   ffffffffa41b4c28   tracepoint_srcu_srcu_usage (mutex)
> 
> The first two were from "task_struct" slab cache.  It happened to
> match with the type name of object but there's no guarantee.  We need
> to add type info to slab cache to resolve the lock inside the object.
> Anyway, the third one has no dedicated slab cache and was allocated by
> kmalloc.
> 
> Those slab objects can be used to filter specific locks using -L or
>  --lock-filter option.  (It needs quotes to avoid special handling in
> the shell).
> 
>     # perf lock con -ab -L '&task_struct' sleep 1
>        contended   total wait     max wait     avg wait         type   caller
> 
>                1     25.10 us     25.10 us     25.10 us        mutex   perf_event_exit_task+0x39
>                1     21.60 us     21.60 us     21.60 us        mutex   futex_exit_release+0x21
>                1      5.56 us      5.56 us      5.56 us        mutex   futex_exec_release+0x21
> 
> The code is available at 'perf/lock-slab-v3' branch in my tree
> 
> git://git.kernel.org/pub/scm/linux/kernel/git/namhyung/linux-perf.git
> 
> Thanks,
> Namhyung
> 
> 
> Namhyung Kim (4):
>   perf lock contention: Add and use LCB_F_TYPE_MASK
>   perf lock contention: Run BPF slab cache iterator
>   perf lock contention: Resolve slab object name using BPF
>   perf lock contention: Handle slab objects in -L/--lock-filter option
> 
>  tools/perf/builtin-lock.c                     |  39 ++++-
>  tools/perf/util/bpf_lock_contention.c         | 140 +++++++++++++++++-
>  .../perf/util/bpf_skel/lock_contention.bpf.c  |  95 +++++++++++-
>  tools/perf/util/bpf_skel/lock_data.h          |  15 +-
>  tools/perf/util/bpf_skel/vmlinux/vmlinux.h    |   8 +
>  tools/perf/util/lock-contention.h             |   2 +
>  6 files changed, 292 insertions(+), 7 deletions(-)
> 
> -- 
> 2.47.1.613.gc27f4b7a9f-goog