Re: [PATCH v3] stdlib: Tuned down tst-arc4random-thread internal parameters

[Szabolcs Nagy <szabolcs.nagy@arm.com>]

The 07/28/2022 09:44, Adhemerval Zanella wrote:
> With new arc4random implementation, the internal parameters might
> require a lot of runtime and/or trigger some contention on older
> kernels (which might trigger spurious timeout failures).
> 
> Also, since we are now testing getrandom entropy instead of an
> userspace RNG, there is no much need to extensive testing.
> 
> With this change the tst-arc4random-thread goes from about 1m to
> 5s on a Ryzen 9 with 5.15.0-41-generic.
> 
> Checked on x86_64-linux-gnu.

thanks, this looks good.

Reviewed-by: Szabolcs Nagy <szabolcs.nagy@arm.com>

> ---
>  stdlib/tst-arc4random-thread.c | 24 ++++++++++++++++++------
>  1 file changed, 18 insertions(+), 6 deletions(-)
> 
> diff --git a/stdlib/tst-arc4random-thread.c b/stdlib/tst-arc4random-thread.c
> index 3373d4d446..daba828fad 100644
> --- a/stdlib/tst-arc4random-thread.c
> +++ b/stdlib/tst-arc4random-thread.c
> @@ -17,23 +17,23 @@
>     <https://www.gnu.org/licenses/>.  */
>  
>  #include <array_length.h>
> +#include <sched.h>
>  #include <stdio.h>
> -#include <string.h>
>  #include <stdlib.h>
> +#include <string.h>
>  #include <support/check.h>
>  #include <support/namespace.h>
>  #include <support/support.h>
>  #include <support/xthread.h>
>  
>  /* Number of arc4random_buf calls per thread.  */
> -enum { count_per_thread = 5000 };
> +enum { count_per_thread = 2048 };
>  
>  /* Number of threads computing randomness.  */
> -enum { inner_threads = 5 };
> +enum { inner_threads = 4 };
>  
> -/* Number of threads launching other threads.  Chosen as to not to
> -   overload the system.  */
> -enum { outer_threads = 7 };
> +/* Number of threads launching other threads.  */
> +static int outer_threads = 1;
>  
>  /* Number of launching rounds performed by the outer threads.  */
>  enum { outer_rounds = 10 };
> @@ -331,6 +331,18 @@ do_test_func (const char *fname, void (*func)(unsigned char *, size_t))
>  static int
>  do_test (void)
>  {
> +  /* Do not run more threads than the maximum of schedulable CPUs.  */
> +  cpu_set_t cpuset;
> +  if (sched_getaffinity (0, sizeof cpuset, &cpuset) == 0)
> +    {
> +      unsigned int ncpus = CPU_COUNT (&cpuset);
> +      /* Limit the number to not overload the system.  */
> +      outer_threads = (ncpus / 2) / inner_threads ?: 1;
> +    }
> +
> +  printf ("info: outer_threads=%d inner_threads=%d\n", outer_threads,
> +	  inner_threads);
> +
>    do_test_func ("arc4random", generate_arc4random);
>    do_test_func ("arc4random_buf", generate_arc4random_buf);
>    do_test_func ("arc4random_uniform", generate_arc4random_uniform);
> -- 
> 2.34.1
>