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
Cc: Song Liu <song@kernel.org>
Cc: bpf@vger.kernel.org
Signed-off-by: Namhyung Kim <namhyung@kernel.org>
1 file changed
