[PATCH v2 02/14] perf trace: Start BPF summary before starting workload

[Ian Rogers <irogers@google.com>]

When using --bpf-summary, trace_start_bpf_summary() sets
skel->bss->enabled = 1. In trace__run(), trace_start_bpf_summary() was
previously invoked after evlist__start_workload().

Because evlist__start_workload() immediately unblocks the child process
by writing to its go_pipe, short-lived workloads (such as `cat /dev/null`)
can execute and complete their initial system calls before
trace_start_bpf_summary() is reached by the parent process. Furthermore,
under high system load, the child process may finish before the BPF
summary tracking is enabled in the kernel at all, causing syscall
summary tests to fail. Additionally, if initial_delay was configured,
the workload was started before sleeping.

Move trace_start_bpf_summary() to be invoked before
evlist__start_workload(), matching evlist__enable(), and ensure it
respects target.initial_delay.

Assisted-by: Antigravity:gemini-3.1-pro
Signed-off-by: Ian Rogers <irogers@google.com>
---
 tools/perf/builtin-trace.c | 8 +++++---
 1 file changed, 5 insertions(+), 3 deletions(-)

diff --git a/tools/perf/builtin-trace.c b/tools/perf/builtin-trace.c
index 20fffc24507b..8da0c51ec380 100644
--- a/tools/perf/builtin-trace.c
+++ b/tools/perf/builtin-trace.c
@@ -4838,17 +4838,19 @@ static int trace__run(struct trace *trace, int argc, const char **argv)
 	if (!target__none(&trace->opts.target) && !trace->opts.target.initial_delay)
 		evlist__enable(evlist);
 
+	if (trace->summary_bpf && !trace->opts.target.initial_delay)
+		trace_start_bpf_summary();
+
 	if (forks)
 		evlist__start_workload(evlist);
 
 	if (trace->opts.target.initial_delay) {
 		usleep(trace->opts.target.initial_delay * 1000);
 		evlist__enable(evlist);
+		if (trace->summary_bpf)
+			trace_start_bpf_summary();
 	}
 
-	if (trace->summary_bpf)
-		trace_start_bpf_summary();
-
 	trace->multiple_threads = perf_thread_map__pid(evlist__core(evlist)->threads, 0) == -1 ||
 		perf_thread_map__nr(evlist__core(evlist)->threads) > 1 ||
 		evlist__first(evlist)->core.attr.inherit;
-- 
2.55.0.1082.g2b9226bbc0-goog