It needs stack traces to find callers of locks.  To minimize the
performance overhead it only collects up to 8 entries for each stack
trace.  And it skips first 3 entries as they came from BPF, tracepoint
and lock functions which are not interested for most users.

But it turned out that those numbers are different in some
configuration.  Using fixed number can result in non meaningful caller
names.  Let's make them adjustable with --stack-depth and --skip-stack
options.

On my setup, the default output is like below:

  # /perf lock con -ab -F contended,wait_total sleep 3
   contended   total wait         type   caller

          28      4.55 ms     rwlock:W   __bpf_trace_contention_begin+0xb
          33      1.67 ms     rwlock:W   __bpf_trace_contention_begin+0xb
          12    580.28 us     spinlock   __bpf_trace_contention_begin+0xb
          60    240.54 us      rwsem:R   __bpf_trace_contention_begin+0xb
          27     64.45 us     spinlock   __bpf_trace_contention_begin+0xb

If I change the stack skip to 5, the result will be like:

  # perf lock con -ab -F contended,wait_total --stack-skip 5 sleep 3
   contended   total wait         type   caller

          32    715.45 us     spinlock   folio_lruvec_lock_irqsave+0x61
          26    550.22 us     spinlock   folio_lruvec_lock_irqsave+0x61
          15    486.93 us      rwsem:R   mmap_read_lock+0x13
          12    139.66 us      rwsem:W   vm_mmap_pgoff+0x93
           1      7.04 us     spinlock   tick_do_update_jiffies64+0x25
Signed-off-by: Namhyung Kim <namhyung@kernel.org>
Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: Ian Rogers <irogers@google.com>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Song Liu <songliubraving@fb.com>
Cc: bpf@vger.kernel.org
Link: https://lore.kernel.org/r/20220912055314.744552-4-namhyung@kernel.orgSigned-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>