Re: [PATCH 6/6] selftests/mm: Don't fail uffd-stress if too many CPUs

[Dev Jain <dev.jain@arm.com>]

On 20/02/25 8:33 pm, Brendan Jackman wrote:
> This calculation divides a fixed parameter by an environment-dependent
> parameter i.e. the number of CPUs.
> 
> The simple way to avoid machine-specific failures here is to just put a
> cap on the max value of the latter.

I haven't read the test, but if nr_cpus is being computed, then this 
value must be important to the test somehow? Would it potentially be 
wrong to let the test run for nr_cpus != actual number of cpus?

Also, if the patch is correct then will it be better to also print a 
diagnostic telling the user that the number of cpus is going to be 
capped for the test to run?

> 
> Suggested-by: Mateusz Guzik <mjguzik@gmail.com>
> Signed-off-by: Brendan Jackman <jackmanb@google.com>
> ---
>   tools/testing/selftests/mm/uffd-stress.c | 4 ++++
>   1 file changed, 4 insertions(+)
> 
> diff --git a/tools/testing/selftests/mm/uffd-stress.c b/tools/testing/selftests/mm/uffd-stress.c
> index 1facfb79e09aa4113e344d7d90dec06a37264058..f306accbef255c79bc3eeba8b9e42161a88fc10e 100644
> --- a/tools/testing/selftests/mm/uffd-stress.c
> +++ b/tools/testing/selftests/mm/uffd-stress.c
> @@ -453,6 +453,10 @@ int main(int argc, char **argv)
>   	}
>   
>   	nr_cpus = sysconf(_SC_NPROCESSORS_ONLN);
> +	if (nr_cpus > 32) {
> +		/* Don't let calculation below go to zero. */
> +		nr_cpus = 32;
> +	}
>   
>   	nr_pages_per_cpu = bytes / page_size / nr_cpus;
>   	if (!nr_pages_per_cpu) {
>