[PATCH] affinity-inheritance: Overallocate CPU sets

[Stefan Liebler]

On 10.01.25 19:01, Siddhesh Poyarekar wrote:
> Some kernels on S390 appear to return a CPU affinity mask based on
> configured processors rather than the ones online.  Overallocate the CPU
> set to match that, but operate only on the ones online.
> 
> Signed-off-by: Siddhesh Poyarekar <siddhesh@sourceware.org>
> ---
>  nptl/tst-skeleton-affinity-inheritance.c | 7 +++++--
>  1 file changed, 5 insertions(+), 2 deletions(-)
> 
> diff --git a/nptl/tst-skeleton-affinity-inheritance.c b/nptl/tst-skeleton-affinity-inheritance.c
> index 6de6d9c942..e6b778e5a7 100644
> --- a/nptl/tst-skeleton-affinity-inheritance.c
> +++ b/nptl/tst-skeleton-affinity-inheritance.c
> @@ -129,13 +129,16 @@ do_one_test (void *arg)
>  static int
>  do_test (void)
>  {
> +  /* Large enough in case the kernel decides to return the larger mask.  This
> +     seems to happen on some kernels for S390x.  */
> +  int num_configured_cpus = get_nprocs_conf ();
>    int num_cpus = get_nprocs ();
>  
>    struct test_param param =
>      {
>        .nproc = num_cpus,
> -      .set = CPU_ALLOC (num_cpus),
> -      .size = CPU_ALLOC_SIZE (num_cpus),
> +      .set = CPU_ALLOC (num_configured_cpus),
> +      .size = CPU_ALLOC_SIZE (num_configured_cpus),
>        .entry = true,
>      };
>  
Hi Siddhesh,

the online vs configured CPUs is the solution as sched_getaffinity
syscall otherwise fails with EINVAL.

But we also have to adjust the other CPU_ALLOCs in the
verify_my_affinity functions. Otherwise the getaffinity functions are
called with size for configured-CPUs but a set only suitable for the
online-CPUs.
With the attached diff on top of your patch, both tests are passing on
my s390x(64bit)/s390(31bit) machines.

Thanks,
Stefan
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