problem in assigning real time scheduling to pthread in linux

[jasdeep_js]

Hi,
I am using RH9-2.4.21 , NPTL version 0.29
I am trying to assign realtime scheduling to the pthreads but facing a strange problem.
I am unable to assign the scheduling policy and priority to a thread while creating it.
after the creation i am able to change its policy and priority (using pthread_setschedparam).
I am working as root .

I even tried with PTHREAD_EXPLICIT_SCHED ,( although this is the default behaviour), but of no use

following is the code :

#include<stdio.h>
#include<pthread.h>
#include<errno.h>
#include<sched.h>

void* CaptureThread()
{
int my_policy;
struct sched_param my_param;
int status;

status = pthread_getschedparam (pthread_self (), &my_policy, &my_param);
printf ("# :thread_routine running at %s/%d\n",
(my_policy == SCHED_FIFO ? "FIFO"
: (my_policy == SCHED_RR ? "RR"
: (my_policy == SCHED_OTHER ? "OTHER"
: "unknown"))),
my_param.sched_priority);

}

pthread_t m_thread;

int main(void)
{

pthread_attr_t thread_attr;
struct sched_param thread_param;
pthread_attr_init(&thread_attr);

pthread_attr_setschedpolicy(&thread_attr, SCHED_RR);
thread_param.sched_priority = 50;
pthread_attr_setschedparam(&thread_attr, &thread_param);
pthread_create(&m_thread, &thread_attr, CaptureThread, NULL);
pthread_join(m_thread,NULL);

}

OUTPUT which i got on running this code :
# :thread_routine running at OTHER/0

here i am just trying to assign scheduling policy as RR and priority 50 and creating a pthread.
Inside the thread function i am printing the sched Policy and priority.
Ideally it should print policy = RR and priority = 50 ; but instead its printing
policy = OTHER and priority = 0

where am i making mistake?

Thanks

[uv256]

#include <stdio.h>
#include <unistd.h>
#include <pthread.h>
#include <sched.h>


void *thread_routine (void *arg)
{
int my_policy;
struct sched_param my_param;


pthread_getschedparam (pthread_self (), &my_policy, &my_param);

printf ("thread_routine running at %s/%d\n",
(my_policy == SCHED_FIFO ? "FIFO"
: (my_policy == SCHED_RR ? "RR"
: (my_policy == SCHED_OTHER ? "OTHER"
: "unknown"))),
my_param.sched_priority);

return NULL;
}

int main (int argc, char *argv[])
{
pthread_t thread_id;
pthread_attr_t thread_attr;
int thread_policy;
struct sched_param thread_param;
int rr_min_priority, rr_max_priority;

pthread_attr_init (&thread_attr);
pthread_attr_getschedpolicy (&thread_attr, &thread_policy);
pthread_attr_getschedparam (&thread_attr, &thread_param);
printf (
"Default policy is %s, priority is %d\n",
(thread_policy == SCHED_FIFO ? "FIFO"
: (thread_policy == SCHED_RR ? "RR"
: (thread_policy == SCHED_OTHER ? "OTHER"
: "unknown"))),
thread_param.sched_priority);

pthread_attr_setschedpolicy (&thread_attr, SCHED_RR);
rr_min_priority = sched_get_priority_min (SCHED_RR);
rr_max_priority = sched_get_priority_max (SCHED_RR);
thread_param.sched_priority =
(rr_min_priority + rr_max_priority)/2;
printf (
"SCHED_RR priority range is %d to %d: using %d\n",
rr_min_priority,
rr_max_priority,
thread_param.sched_priority);
pthread_attr_setschedparam (&thread_attr, &thread_param);

printf (
"Creating thread at RR/%d\n",
thread_param.sched_priority);
pthread_attr_setinheritsched (&thread_attr, PTHREAD_EXPLICIT_SCHED);
pthread_create (&thread_id, &thread_attr, thread_routine, NULL);
pthread_join (thread_id, NULL);
return 0;
}

[uv256]

so you basically forgot to add this line before pthread_create
pthread_attr_setinheritsched (&thread_attr, PTHREAD_EXPLICIT_SCHED);

[indrasakti]

Hi..

i think we can simulate preemption by using 2 different priority thread, am i true? I just try these scenario :
1. Create Thread A with priority 99 , SCHED_FIFO..
2. Create Thread B with priority 4 , SCHED_FIFO

Thread A started and doing some busy work.. I guest that Thread B wouldn't start until thread A finished, but I get thread B can run before Thread A finished (It just like a common task switching).. I'm sure my 2 thread has right priority.

Can anyone help me?