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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 <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 <songliubraving@fb.com>
Cc: bpf@vger.kernel.org
Link: https://lore.kernel.org/r/20220912055314.744552-5-namhyung@kernel.org
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>
This commit is contained in:
Namhyung Kim 2022-09-11 22:53:14 -07:00 committed by Arnaldo Carvalho de Melo
parent 96532a83ee
commit c1da8dd5c1
2 changed files with 6 additions and 4 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

7
tools/perf/util/bpf_lock_contention.c
View File

@ -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++;

3
tools/perf/util/bpf_skel/lock_contention.bpf.c
View File

@ -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++;