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

[Shizhao Chen]

Thanks for the review! I just sent a v2 which is basically a minimized
version of tst_ncpus_available.

On Wed, Jul 10, 2024 at 2:27 PM Li Wang <liwang@redhat.com> wrote:
>
>
>
> On Wed, Jul 10, 2024 at 2:13 PM Li Wang <liwang@redhat.com> wrote:
>>
>> 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.
>
>
> Oops, seems the real-time tests does not include ltp library.
> So you patch make sense from this point, but maybe we
> need to refine the function to consider more situations.
>
> e.g. uses a fixed-size cpu_set_t structure, which might not be
> sufficient on systems with a large number of CPUs.
>
>
>>
>>
>> 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
>
>
>
> --
> Regards,
> Li Wang