Commit c940fa27 authored by Namhyung Kim's avatar Namhyung Kim Committed by Arnaldo Carvalho de Melo

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: default avatarNamhyung 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: default avatarArnaldo Carvalho de Melo <acme@redhat.com>
parent 9e9c5f3c
......@@ -91,7 +91,7 @@ struct thread_stat {
* Number of stack trace entries to skip when finding callers.
* The first few entries belong to the locking implementation itself.
*/
#define CONTENTION_STACK_SKIP 3
#define CONTENTION_STACK_SKIP 4
/*
* flags for lock:contention_begin
......
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