[LTP] [RFC] [PATCH] sched: starvation: Autocallibrate the timeout

[Cyril Hrubis]

Instead of hardcoding the values we attempt to measure the CPU speed and
set the timeout accordingly. Given that the difference in the duration
of the test when the kernel is buggy is about 30x we do not have to have
a precise callibration, just very rough estimate if we are running on a
server or small ARM board would suffice.

So we attempt to measure how long does a bussy loop take and base the
default timeout on that. On x86_64 CPUs the resulting timeout is about
double of the value of the actual test runtime and works fine, but we
need to make sure that the coeficient we divide the result from
callibrate works for small boards too. So please run the test on as many
machines as you can and report if we need to make the dividor smaller or
not.

CC: Steve <xufeifei1@oppo.com>
Signed-off-by: Cyril Hrubis <chrubis@suse.cz>
---
 .../kernel/sched/cfs-scheduler/starvation.c   | 40 +++++++++++++++++--
 1 file changed, 37 insertions(+), 3 deletions(-)

diff --git a/testcases/kernel/sched/cfs-scheduler/starvation.c b/testcases/kernel/sched/cfs-scheduler/starvation.c
index eb9fd6ff5..94175fdd1 100644
--- a/testcases/kernel/sched/cfs-scheduler/starvation.c
+++ b/testcases/kernel/sched/cfs-scheduler/starvation.c
@@ -21,11 +21,42 @@
 #include <sched.h>
 
 #include "tst_test.h"
+#include "tst_safe_clocks.h"
+#include "tst_timer.h"
 
 static char *str_loop;
-static long loop = 2000000;
+static long loop = 1000000;
 static char *str_timeout;
-static int timeout = 240;
+static int timeout;
+
+#define CALLIBRATE_LOOPS 100000000
+
+static int callibrate(void)
+{
+	volatile int counter;
+	struct timespec start, stop;
+	long long diff;
+
+	counter = CALLIBRATE_LOOPS;
+	do
+		counter--;
+	while (counter > 0);
+
+	SAFE_CLOCK_GETTIME(CLOCK_MONOTONIC_RAW, &start);
+
+	counter = CALLIBRATE_LOOPS;
+	do
+		counter--;
+	while (counter > 0);
+
+	SAFE_CLOCK_GETTIME(CLOCK_MONOTONIC_RAW, &stop);
+
+	diff = tst_timespec_diff_us(stop, start);
+
+	tst_res(TINFO, "CPU did %i loops in %llius", CALLIBRATE_LOOPS, diff);
+
+	return diff;
+}
 
 static int wait_for_pid(pid_t pid)
 {
@@ -59,8 +90,11 @@ static void setup(void)
 	if (tst_parse_long(str_loop, &loop, 1, LONG_MAX))
 		tst_brk(TBROK, "Invalid number of loop number '%s'", str_loop);
 
-	if (tst_parse_int(str_timeout, &timeout, 1, INT_MAX))
+	if (tst_parse_int(str_timeout, &timeout, 1, INT_MAX)) {
 		tst_brk(TBROK, "Invalid number of timeout '%s'", str_timeout);
+	} else {
+		timeout = callibrate() / 1000;
+	}
 
 	tst_set_max_runtime(timeout);
 }
-- 
2.44.2