The -S/--callstack-filter is to limit display entries having the given
string in the callstack (not only in the caller in the output).

The following example shows lock contention results if the callstack
has 'net' substring somewhere.  Note that the caller '__dev_queue_xmit'
does not match to it, but it has 'inet6_csk_xmit' in the callstack.

This applies even if you don't use -v option to show the full callstack.

  $ sudo ./perf lock con -abv -S net sleep 1
  ...
   contended   total wait     max wait     avg wait         type   caller

           5     70.20 us     16.13 us     14.04 us     spinlock   __dev_queue_xmit+0xb6d
                          0xffffffffa5dd1c60  _raw_spin_lock+0x30
                          0xffffffffa5b8f6ed  __dev_queue_xmit+0xb6d
                          0xffffffffa5cd8267  ip6_finish_output2+0x2c7
                          0xffffffffa5cdac14  ip6_finish_output+0x1d4
                          0xffffffffa5cdb477  ip6_xmit+0x457
                          0xffffffffa5d1fd17  inet6_csk_xmit+0xd7
                          0xffffffffa5c5f4aa  __tcp_transmit_skb+0x54a
                          0xffffffffa5c6467d  tcp_keepalive_timer+0x2fd
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 <song@kernel.org>
Cc: bpf@vger.kernel.org
Link: https://lore.kernel.org/r/20230126000936.3017683-1-namhyung@kernel.orgSigned-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>