From: Ian Rogers <irogers@google.com>
Date: Tue, 2 Jun 2026 17:41:15 +0000 (-0700)
Subject: perf test: Drain pipe after child finishes to avoid losing output
X-Git-Url: http://git.ipfire.org/gitweb.cgi?a=commitdiff_plain;h=744af598719776b2ca8b0f5388b51d2493cc94b7;p=thirdparty%2Fkernel%2Flinux.git

perf test: Drain pipe after child finishes to avoid losing output

When running tests in parallel, the parent process reads output from the
child's pipe. However, it might exit the loop as soon as the child is
detected as finished, potentially missing data that arrived in the pipe
just after the last poll or before the loop terminated.

Address this by draining the pipe after the main loop in finish_test.

Assisted-by: Gemini-CLI:Google Gemini 3
Signed-off-by: Ian Rogers <irogers@google.com>
Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: James Clark <james.clark@linaro.org>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>
---

diff --git a/tools/perf/tests/builtin-test.c b/tools/perf/tests/builtin-test.c
index f2c135891477c..7946878195b7d 100644
--- a/tools/perf/tests/builtin-test.c
+++ b/tools/perf/tests/builtin-test.c
@@ -483,6 +483,16 @@ static void finish_test(struct child_test **child_tests, int running_test, int c
 		if (err_done)
 			err_done = check_if_command_finished(&child_test->process);
 	}
+	/* Drain any remaining data from the pipe. */
+	if (err > 0) {
+		char buf[512];
+		ssize_t len;
+
+		while ((len = read(err, buf, sizeof(buf) - 1)) > 0) {
+			buf[len] = '\0';
+			strbuf_addstr(&err_output, buf);
+		}
+	}
 	if (perf_use_color_default && last_running != -1) {
 		/* Erase "Running (.. active)" line printed before poll/sleep. */
 		fprintf(debug_file(), PERF_COLOR_DELETE_LINE);