The context :
We are designing a realtime Radio Link Control driver with hard real time
constraints.
We launch 2 threads on a bi processor, 1 thread on P1, 1 thread on P2.
Both threads run in an infinite loop and both are periodic (10 milli
seconds).
Both treads try to lock a mutex, make a few code then unlock the mutex (they
try to access a shared list protected by a mutex).
The execution time of the code between the lock and the unlock of the mutex
is no more than a few micro seconds.
But when I mesure the execution time of the code that lock, process, and
then unlock the mutex with the help of the function clock_gethrtime(), I can
notice than sometimes it take 5 milli seconds (the value is nearly always
the same : 5ms +/- a few micro seconds) ???.
Any help would be appreciated.
Thanks.
-----------------------------------------------------
Hardware : Bi processor PIII 1 GHz 512Mo
-----------------------------------------------------
Software :
Redhat 7.1
Kernel 2.4.4 from kernel.org
RT-Linux 3.1
-----------------------------------------------------
Code for thread 1 (idem for thread 2 except counter2):
void *thread_test1(void* notusedP) {
hrtime_t start, end, process;
pthread_make_periodic_np(pthread_self(), gethrtime(), 10000000); /* 10
milli seconds */
while (1) {
start = gethrtime();
/* code that acquire a mutex here not detailled */
end = gethrtime();
process = end - start;
if (process > 1000000) { /* 1 milli second */
counter1+=1; // extern variable displayed when cleaning up the module
}
pthread_wait_np();
}
}
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