[LTP] [PATCH] clock_gettime04: set threshold based on the clock tick rate

[Li Wang <liwang@redhat.com>]

This is to get rid of the intermittent failures in clock_gettime04,
which are likely caused by different clock tick rates on platforms.
Here set the threshold no less than each clock tick in millisecond:

	delta = 1000(ms)/ticks_number_per_sec + 5;

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>
---
 testcases/kernel/syscalls/clock_gettime/clock_gettime04.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/testcases/kernel/syscalls/clock_gettime/clock_gettime04.c b/testcases/kernel/syscalls/clock_gettime/clock_gettime04.c
index a8d2c5b38..cccbc9383 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;
 
 static inline int do_vdso_gettime(gettime_t vdso, clockid_t clk_id, void *ts)
 {
@@ -92,6 +92,7 @@ static struct time64_variants variants[] = {
 
 static void setup(void)
 {
+	delta = 1000/sysconf(_SC_CLK_TCK) + 5;
 	if (tst_is_virt(VIRT_ANY)) {
 		tst_res(TINFO, "Running in a virtual machine, multiply the delta by 10.");
 		delta *= 10;
-- 
2.31.1


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