[PATCH] tests: posix: use cpu clock for sleep

[Florian Weimer]

* Yury Khrustalev:

> On some emulated targets sleep may result in inconsistent wait
> times which will lead to the failure of the tst-chmod test.
>
> To account for this we use the CLOCK_PROCESS_CPUTIME_ID clock ID
> while also consuming CPU time by repeatedly calling clock_gettime.
>
> ---
> Passes regression on aarch64 and x86. OK for trunk?
> Base commit: 67494ceb5d
>
> ---
>  posix/tst-chmod.c | 19 +++++++++++++++++--
>  1 file changed, 17 insertions(+), 2 deletions(-)
>
> diff --git a/posix/tst-chmod.c b/posix/tst-chmod.c
> index 80a69dddd4..620055080c 100644
> --- a/posix/tst-chmod.c
> +++ b/posix/tst-chmod.c
> @@ -26,6 +26,7 @@
>  #include <string.h>
>  #include <unistd.h>
>  #include <sys/stat.h>
> +#include <time.h>
>  
>  #include <support/xunistd.h>
>  
> @@ -37,6 +38,20 @@
>      goto fail;								      \
>    } while (0)
>  
> +/* On some emulated targets sleep may result in inconsistent wait
> +   times which will lead to the failure of this test.  To account
> +   for this we use the CLOCK_PROCESS_CPUTIME_ID clock ID while
> +   also consuming CPU time by repeatedly calling clock_gettime. */
> +static void
> +test_sleep (unsigned long seconds)
> +{
> +  struct timespec ts;
> +  clock_gettime (CLOCK_PROCESS_CPUTIME_ID, &ts);
> +  unsigned long end = ts.tv_sec + seconds;
> +  while (ts.tv_sec < end)
> +    clock_gettime (CLOCK_PROCESS_CPUTIME_ID, &ts);
> +}

This can wait a very short time only if tv_nsec is close to the maximum.

How accurate is CLOCK_PROCESS_CPUTIME_ID on emulated targets?  Should we
busy-wait and also wait for the wall clock time to increase?

Thanks,
Florian