[LTP] [PATCH v2] clock_gettime04: set threshold based on the clock resolution

[Li Wang]

This is to get rid of the intermittent failures in clock_gettime04,
which are likely caused by different clock tick rates on platforms.
Here give two thresholds (in milliseconds) for comparison, one for
COARSE clock and one for the rest.

Error log:
  clock_gettime04.c:163: TFAIL: CLOCK_REALTIME_COARSE(syscall with old kernel spec):
        Difference between successive readings greater than 5 ms (1): 10
  clock_gettime04.c:163: TFAIL: CLOCK_MONOTONIC_COARSE(vDSO with old kernel spec):
	Difference between successive readings greater than 5 ms (2): 10

>From Waiman Long:
  That failure happens for CLOCK_REALTIME_COARSE which is a faster but less
  precise version of CLOCK_REALTIME. The time resolution is actually a clock
  tick. Since arm64 has a HZ rate of 100. That means each tick is 10ms. So a
  CLOCK_REALTIME_COARSE threshold of 5ms is probably not enough. I would say
  in the case of CLOCK_REALTIME_COARSE, we have to increase the threshold based
  on the clock tick rate of the system. This is more a test failure than is
  an inherent problem in the kernel.

Fixes #898

Reported-by: Eirik Fuller <efuller@redhat.com>
Signed-off-by: Li Wang <liwang@redhat.com>
Cc: Waiman Long <llong@redhat.com>
Cc: Viresh Kumar <viresh.kumar@linaro.org>
---

Notes:
    v1 --> v2
        * make use of clock_getres to get clock resolution
        * involve separate coarse_delta for COARSE clock
        * count delta as 'clock resolution + elapse (5ms)'

 .../syscalls/clock_gettime/clock_gettime04.c   | 18 ++++++++++++++++--
 1 file changed, 16 insertions(+), 2 deletions(-)

diff --git a/testcases/kernel/syscalls/clock_gettime/clock_gettime04.c b/testcases/kernel/syscalls/clock_gettime/clock_gettime04.c
index a8d2c5b38..c279da79e 100644
--- a/testcases/kernel/syscalls/clock_gettime/clock_gettime04.c
+++ b/testcases/kernel/syscalls/clock_gettime/clock_gettime04.c
@@ -35,7 +35,7 @@ clockid_t clks[] = {
 };
 
 static gettime_t ptr_vdso_gettime, ptr_vdso_gettime64;
-static long long delta = 5;
+static long long delta, precise_delta, coarse_delta;
 
 static inline int do_vdso_gettime(gettime_t vdso, clockid_t clk_id, void *ts)
 {
@@ -92,9 +92,18 @@ static struct time64_variants variants[] = {
 
 static void setup(void)
 {
+	struct timespec res;
+
+	clock_getres(CLOCK_REALTIME, &res);
+	precise_delta = 5 + res.tv_nsec / 1000000;
+
+	clock_getres(CLOCK_REALTIME_COARSE, &res);
+	coarse_delta = 5 + res.tv_nsec / 1000000;
+
 	if (tst_is_virt(VIRT_ANY)) {
 		tst_res(TINFO, "Running in a virtual machine, multiply the delta by 10.");
-		delta *= 10;
+		precise_delta *= 10;
+		coarse_delta *= 10;
 	}
 
 	find_clock_gettime_vdso(&ptr_vdso_gettime, &ptr_vdso_gettime64);
@@ -108,6 +117,11 @@ static void run(unsigned int i)
 	int count = 10000, ret;
 	unsigned int j;
 
+	if (clks[i] == CLOCK_REALTIME_COARSE || clks[i] == CLOCK_MONOTONIC_COARSE)
+		delta = coarse_delta;
+	else
+		delta = precise_delta;
+
 	do {
 		for (j = 0; j < ARRAY_SIZE(variants); j++) {
 			/* Refresh time in start */
-- 
2.31.1