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

[Li Wang]

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