From c1da8dd5c11dabd50b1578c6b43d73c7bbc28963 Mon Sep 17 00:00:00 2001 From: Namhyung Kim Date: Sun, 11 Sep 2022 22:53:14 -0700 Subject: [PATCH] perf lock contention: Skip stack trace from BPF Currently it collects stack traces to max size then skip entries. Because we don't have control how to skip perf callchains. But BPF can do it with bpf_get_stackid() with a flag. Say we have max-stack=4 and stack-skip=2, we get these stack traces. Before: After: .---> +---+ <--. .---> +---+ <--. | | | | | | | | | +---+ usable | +---+ | max | | | max | | | stack +---+ <--' stack +---+ usable | | X | | | | | | +---+ skip | +---+ | | | X | | | | | `---> +---+ `---> +---+ <--' <=== collection | X | +---+ skip | X | +---+ Signed-off-by: Namhyung Kim Cc: Adrian Hunter Cc: Ian Rogers Cc: Ingo Molnar Cc: Jiri Olsa Cc: Peter Zijlstra Cc: Song Liu Cc: bpf@vger.kernel.org Link: https://lore.kernel.org/r/20220912055314.744552-5-namhyung@kernel.org Signed-off-by: Arnaldo Carvalho de Melo --- tools/perf/util/bpf_lock_contention.c | 7 ++++--- tools/perf/util/bpf_skel/lock_contention.bpf.c | 3 ++- 2 files changed, 6 insertions(+), 4 deletions(-) diff --git a/tools/perf/util/bpf_lock_contention.c b/tools/perf/util/bpf_lock_contention.c index ef5323c78ffc..efe5b9968e77 100644 --- a/tools/perf/util/bpf_lock_contention.c +++ b/tools/perf/util/bpf_lock_contention.c @@ -93,6 +93,8 @@ int lock_contention_prepare(struct lock_contention *con) bpf_map_update_elem(fd, &pid, &val, BPF_ANY); } + skel->bss->stack_skip = con->stack_skip; + lock_contention_bpf__attach(skel); return 0; } @@ -127,7 +129,7 @@ int lock_contention_read(struct lock_contention *con) while (!bpf_map_get_next_key(fd, &prev_key, &key)) { struct map *kmap; struct symbol *sym; - int idx; + int idx = 0; bpf_map_lookup_elem(fd, &key, &data); st = zalloc(sizeof(*st)); @@ -146,8 +148,7 @@ int lock_contention_read(struct lock_contention *con) bpf_map_lookup_elem(stack, &key, stack_trace); - /* skip BPF + lock internal functions */ - idx = con->stack_skip; + /* skip lock internal functions */ while (is_lock_function(machine, stack_trace[idx]) && idx < con->max_stack - 1) idx++; diff --git a/tools/perf/util/bpf_skel/lock_contention.bpf.c b/tools/perf/util/bpf_skel/lock_contention.bpf.c index 9e8b94eb6320..e107d71f0f1a 100644 --- a/tools/perf/util/bpf_skel/lock_contention.bpf.c +++ b/tools/perf/util/bpf_skel/lock_contention.bpf.c @@ -72,6 +72,7 @@ struct { int enabled; int has_cpu; int has_task; +int stack_skip; /* error stat */ unsigned long lost; @@ -117,7 +118,7 @@ int contention_begin(u64 *ctx) pelem->timestamp = bpf_ktime_get_ns(); pelem->lock = (__u64)ctx[0]; pelem->flags = (__u32)ctx[1]; - pelem->stack_id = bpf_get_stackid(ctx, &stacks, BPF_F_FAST_STACK_CMP); + pelem->stack_id = bpf_get_stackid(ctx, &stacks, BPF_F_FAST_STACK_CMP | stack_skip); if (pelem->stack_id < 0) lost++;