thread scheduling priority

[Petri Helenius]

I have two threads on a SMP (2 CPU, HT disabled) box with world+kernel
from mid-June. (cvsupping to latest right now) and a process which
runs two threads with the following code snippet, more or less in a process
& maintenance (collecting statistics, doing housekeeping, etc.) fashion. 
While
the main thread does it's stuff it competes for a mutex with the other 
thread. However
I'm observing that the thread created in the snippet below has hard time 
getting
scheduled  while the main thread is running.

Am I missing something? No rtprio stuff here, contention scope is the 
default.

  {
    struct sched_param param;
    pthread_attr_t attributes;

    pthread_attr_init (&attributes);
    pthread_attr_getschedparam (&attributes,&param);
    param.sched_priority += 5;
    pthread_attr_setschedparam (&attributes,&param);
    pthread_create (&smem_thread,&attributes,&live_poll_sharedmem,0);
 }
 
Pete