perf test: Add 'sqrtloop' test workload

The sqrtloop creates a child process to run an infinite loop calling
sqrt() with rand().  This is needed for ARM SPE fork test.

  $ perf test -w sqrtloop

It can take an optional argument to specify how long it will run in
seconds (default: 1).

Committer notes:

Explicitely ignored the sqrt() return to fix the build on systems where
the compiler complains it isn't being used.

And added a sqrtloop specific CFLAGS to disable optimizations to make
this a bit more robust wrt dead code elimination.

Doing that a -U_FORTIFY_SOURCE needs to be added, as -O0 is incompatible
with it.

Signed-off-by: Namhyung Kim <namhyung@kernel.org>
Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: Athira Jajeev <atrajeev@linux.vnet.ibm.com>
Cc: German Gomez <german.gomez@arm.com>
Cc: Ian Rogers <irogers@google.com>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: James Clark <james.clark@arm.com>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Leo Yan <leo.yan@linaro.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Zhengjun Xing <zhengjun.xing@linux.intel.com>
Link: https://lore.kernel.org/r/20221116233854.1596378-8-namhyung@kernel.org
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

tools/perf/tests/builtin-test.c

@@ -122,6 +122,7 @@ static struct test_workload *workloads[] = {
 	&workload__noploop,
 	&workload__thloop,
 	&workload__leafloop,
+	&workload__sqrtloop,
 };
 
 static int num_subtests(const struct test_suite *t)

tools/perf/tests/tests.h

@@ -203,5 +203,6 @@ struct test_workload workload__##work = {	\
 DECLARE_WORKLOAD(noploop);
 DECLARE_WORKLOAD(thloop);
 DECLARE_WORKLOAD(leafloop);
+DECLARE_WORKLOAD(sqrtloop);
 
 #endif /* TESTS_H */

tools/perf/tests/workloads/Build

@@ -3,5 +3,7 @@
 perf-y += noploop.o
 perf-y += thloop.o
 perf-y += leafloop.o
+perf-y += sqrtloop.o
 
+CFLAGS_sqrtloop.o         = -g -O0 -fno-inline -U_FORTIFY_SOURCE
 CFLAGS_leafloop.o         = -g -O0 -fno-inline -fno-omit-frame-pointer -U_FORTIFY_SOURCE

tools/perf/tests/workloads/sqrtloop.c

@@ -0,0 +1,45 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+#include <math.h>
+#include <signal.h>
+#include <stdlib.h>
+#include <unistd.h>
+#include <linux/compiler.h>
+#include <sys/wait.h>
+#include "../tests.h"
+
+static volatile sig_atomic_t done;
+
+static void sighandler(int sig __maybe_unused)
+{
+	done = 1;
+}
+
+static int __sqrtloop(int sec)
+{
+	signal(SIGALRM, sighandler);
+	alarm(sec);
+
+	while (!done)
+		(void)sqrt(rand());
+	return 0;
+}
+
+static int sqrtloop(int argc, const char **argv)
+{
+	int sec = 1;
+
+	if (argc > 0)
+		sec = atoi(argv[0]);
+
+	switch (fork()) {
+	case 0:
+		return __sqrtloop(sec);
+	case -1:
+		return -1;
+	default:
+		wait(NULL);
+	}
+	return 0;
+}
+
+DEFINE_WORKLOAD(sqrtloop);