[LTP] [PATCH] realtime/prio-preempt: take cpu isolation into consideration

[Li Wang]

Hi Shizhao,

On Wed, Jul 10, 2024 at 11:24 AM Shizhao Chen <shichen@redhat.com> wrote:

> By default the test starts N-1 busy threads to monopolize N-1 available
> CPUs,
> where N is the number of all available CPUs. However, when CPU isolation is
> applied, this will lead to a hang scenario where all housekeeping CPUs are
> hogged as isolated CPUs do not share the N-1 busy threads.
>
> Signed-off-by: Shizhao Chen <shichen@redhat.com>
> ---
>  .../realtime/func/prio-preempt/prio-preempt.c  | 18 +++++++++++++++---
>  1 file changed, 15 insertions(+), 3 deletions(-)
>
> diff --git a/testcases/realtime/func/prio-preempt/prio-preempt.c
> b/testcases/realtime/func/prio-preempt/prio-preempt.c
> index 9bd5e7ad8..79d2115a7 100644
> --- a/testcases/realtime/func/prio-preempt/prio-preempt.c
> +++ b/testcases/realtime/func/prio-preempt/prio-preempt.c
> @@ -59,6 +59,7 @@
>   *
>
> *****************************************************************************/
>
> +#define _GNU_SOURCE
>  #include <stdio.h>
>  #include <stdlib.h>
>  #include <signal.h>
> @@ -287,6 +288,17 @@ void *master_thread(void *arg)
>         return NULL;
>  }
>
> +int get_numcpus(void)
> +{
> +       cpu_set_t mask;
> +       CPU_ZERO(&mask);
> +
> +       /* Get the number of cpus accessible to the current process */
> +       sched_getaffinity(getpid(), sizeof(mask), &mask);
> +
> +       return CPU_COUNT(&mask);
> +}

+
>  int main(int argc, char *argv[])
>  {
>         int pri_boost, numcpus;
> @@ -295,10 +307,10 @@ int main(int argc, char *argv[])
>         pass_criteria = CHECK_LIMIT;
>         rt_init("hin:", parse_args, argc, argv);
>
> -       numcpus = sysconf(_SC_NPROCESSORS_ONLN);
> +       numcpus = get_numcpus();
>

Maybe we could make use of LTP lib function tst_ncpus_available directly?
Seems the new get_numcpus() did a dup work on that.

Otherwise, looks good to me.


> -       /* Max no. of busy threads should always be less than/equal the
> no. of cpus
> -          Otherwise, the box will hang */
> +       /* Max no. of busy threads should always be less than/equal the
> no. of
> +          housekeeping cpus. Otherwise, the box will hang */
>
>         if (rt_threads == -1 || rt_threads > numcpus) {
>                 rt_threads = numcpus;
> --
> 2.45.2
>
>

-- 
Regards,
Li Wang