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

[Waiman Long]

On 3/29/22 01:03, Li Wang wrote:
> 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;
>   	}

The patch looks good in general. However, maybe we should do something like:

diff --git a/clock_gettime04.c b/clock_gettime04.c
index a8d2c5b..1ba218b 100644
--- a/clock_gettime04.c
+++ b/clock_gettime04.c
@@ -92,11 +92,18 @@ static struct time64_variants variants[] = {

  static void setup(void)
  {
+       delta = 5;
         if (tst_is_virt(VIRT_ANY)) {
                 tst_res(TINFO, "Running in a virtual machine, multiply 
the delta by 10.");
                 delta *= 10;
         }

+       clock_getres(CLOCK_REALTIME, &res);
+       precise_delta = delta + res.tv_nsec / 1000000;
+
+       clock_getres(CLOCK_REALTIME_COARSE, &res);
+       coarse_delta = delta + res.tv_nsec / 1000000;
+
         find_clock_gettime_vdso(&ptr_vdso_gettime, &ptr_vdso_gettime64);
  }

to avoid a coarse_delta that is too large for vm.

Cheers,
Longman