perf lock contention: Increase default stack skip to 4
In most configurations, it works well with skipping 4 entries by default. If some systems still have 3 BPF internal stack frames, the next frame should be in a lock function which will be skipped later when it tries to find a caller. So increasing to 4 won't affect such systems too. With --stack-skip=0, I can see something like this: 24 49.84 us 7.41 us 2.08 us mutex bpf_prog_e1b85959d520446c_contention_begin+0x12e 0xffffffffc045040e bpf_prog_e1b85959d520446c_contention_begin+0x12e 0xffffffffc045040e bpf_prog_e1b85959d520446c_contention_begin+0x12e 0xffffffff82ea2071 bpf_trace_run2+0x51 0xffffffff82de775b __bpf_trace_contention_begin+0xb 0xffffffff82c02045 __mutex_lock+0x245 0xffffffff82c019e3 __mutex_lock_slowpath+0x13 0xffffffff82c019c0 mutex_lock+0x20 0xffffffff830a083c kernfs_iop_permission+0x2c 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/20221028180128.3311491-5-namhyung@kernel.orgSigned-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>
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