[ECOS] Thread related queries

[ECOS] Thread related queries

[Jaiprakash]

Hello,
I have the following queries regarding implementation of threading in 
ecos:
 
1. Does ecos consider main() as a running thread or is it just an entry 
point to the system.
2. What is Cyg_Idle_thread used for? its functionality is not clear.
3. I was trying to compare following piece of code on linux 6.2 and 
ecos running on my board.
 
 
#include <pthread.h>
#include <signal.h>
#define NUM_THREADS     3

void *PrintThreadid(void *threadid)
{
  int i;
  for(;;){
      printf("\nthread %d\n",threadid);
      i = sleep(1);  
      if(i) {
           printf("return value from sleep() %d", i);
      }
  }
}

int main()
{
    pthread_t threads[NUM_THREADS];
    int rc, t,i,j;
    int *thread_return;
    pthread_attr_t attr;
 
    rc =  pthread_attr_init(&attr);
    if(rc){
       printf("ERROR: return code from pthread_attr_init %d", rc);
    } 
    printf("\n creating threads\n");  
    for(t=0;t < NUM_THREADS;t++){
        rc = pthread_create(&threads[t], &attr, PrintThreadid, (void *)
t);
        if (rc){
             printf("ERROR; return code from pthread_create()%d ", rc);
        }
   }
    printf("\n running main thread\n");
    pthread_attr_destroy(&attr);
    for(t=0;t < NUM_THREADS;t++){
        rc = pthread_join(threads[t], (void *)&thread_return); 
        if(rc){
           printf("ERROR: return code from pthread_join %d", rc);
        }
        printf("Completed join with thread %d thread_return = %d\n",t, 
thread_return );
    }
    
    while(1) ;
}

 
 
On linux the control goes to main() once, later the threads keep 
running continuously. But in ecos the main() seems to get more 
timeslice (15 - 20 times more) than the three threads. My basic clock 
tick is 0.5 secs and timeslicing is 2 ticks. can you give me some 
inputs regarding the difference of behaviour eventhough i am using 
pthread calls. 
There is not much documentation regarding implementation of threading 
in ecos.
 
Thanking you in advance.
 
Jaiprakash N

RE: [ECOS] Thread related queries

[Trenton D. Adams]

See "Thread Operations" in the eCos Reference guide.  Then take a look
at "ecos/examples/twothreads.c" one directory below the root of your
repository.  That is to say the directory with "packages", and "host"
directories in it.

-----Original Message-----
From: ecos-discuss-owner@sources.redhat.com
[ mailto:ecos-discuss-owner@sources.redhat.com ] On Behalf Of Jaiprakash
Sent: Saturday, August 25, 2001 5:35 AM
To: ecos-discuss@sources.redhat.com
Subject: [ECOS] Thread related queries



Hello,
I have the following queries regarding implementation of threading in 
ecos:
 
1. Does ecos consider main() as a running thread or is it just an entry 
point to the system.
2. What is Cyg_Idle_thread used for? its functionality is not clear.
3. I was trying to compare following piece of code on linux 6.2 and 
ecos running on my board.
 
 
#include <pthread.h>
#include <signal.h>
#define NUM_THREADS     3

void *PrintThreadid(void *threadid)
{
  int i;
  for(;;){
      printf("\nthread %d\n",threadid);
      i = sleep(1);  
      if(i) {
           printf("return value from sleep() %d", i);
      }
  }
}

int main()
{
    pthread_t threads[NUM_THREADS];
    int rc, t,i,j;
    int *thread_return;
    pthread_attr_t attr;
 
    rc =  pthread_attr_init(&attr);
    if(rc){
       printf("ERROR: return code from pthread_attr_init %d", rc);
    } 
    printf("\n creating threads\n");  
    for(t=0;t < NUM_THREADS;t++){
        rc = pthread_create(&threads[t], &attr, PrintThreadid, (void *)
t);
        if (rc){
             printf("ERROR; return code from pthread_create()%d ", rc);
        }
   }
    printf("\n running main thread\n");
    pthread_attr_destroy(&attr);
    for(t=0;t < NUM_THREADS;t++){
        rc = pthread_join(threads[t], (void *)&thread_return); 
        if(rc){
           printf("ERROR: return code from pthread_join %d", rc);
        }
        printf("Completed join with thread %d thread_return = %d\n",t, 
thread_return );
    }
    
    while(1) ;
}

 
 
On linux the control goes to main() once, later the threads keep 
running continuously. But in ecos the main() seems to get more 
timeslice (15 - 20 times more) than the three threads. My basic clock 
tick is 0.5 secs and timeslicing is 2 ticks. can you give me some 
inputs regarding the difference of behaviour eventhough i am using 
pthread calls. 
There is not much documentation regarding implementation of threading 
in ecos.
 
Thanking you in advance.
 
Jaiprakash N

Re: [ECOS] Thread related queries

[Jonathan Larmour]

Jaiprakash wrote:
> On linux the control goes to main() once, later the threads keep
> running continuously. But in ecos the main() seems to get more
> timeslice (15 - 20 times more) than the three threads. My basic clock
> tick is 0.5 secs and timeslicing is 2 ticks. can you give me some
> inputs regarding the difference of behaviour eventhough i am using
> pthread calls.

eCos is a real-time system (which Linux is not), which means you have to be
concerned about the thread priorities. A higher priority thread will get
all the CPU, unless it has been blocked for some reason. main()'s (eCos)
priority is set with the configuration variable
CYGNUM_POSIX_MAIN_DEFAULT_PRIORITY, and defaults to 30.

Unfortunately, a POSIX thread has a default POSIX priority of 0, which
translates to an ECOS_PRIORITY of (CYG_THREAD_MIN_PRIORITY-priority) i.e.
31. Not only is this less than main's, it is the same as the idle thread,
meaning it will be timeslicing with it.

I think instead sched_priority in pthread_attr_init() should default to 1.
Nick, know any reason why not?

Jifl
-- 
Red Hat, Rustat House, Clifton Road, Cambridge, UK. Tel: +44 (1223) 271062
Maybe this world is another planet's Hell -Aldous Huxley || Opinions==mine

Re: [ECOS] Thread related queries

[Nick Garnett]

Jonathan Larmour <jlarmour@redhat.com> writes:

> Jaiprakash wrote:
> > On linux the control goes to main() once, later the threads keep
> > running continuously. But in ecos the main() seems to get more
> > timeslice (15 - 20 times more) than the three threads. My basic clock
> > tick is 0.5 secs and timeslicing is 2 ticks. can you give me some
> > inputs regarding the difference of behaviour eventhough i am using
> > pthread calls.
> 
> eCos is a real-time system (which Linux is not), which means you have to be
> concerned about the thread priorities. A higher priority thread will get
> all the CPU, unless it has been blocked for some reason. main()'s (eCos)
> priority is set with the configuration variable
> CYGNUM_POSIX_MAIN_DEFAULT_PRIORITY, and defaults to 30.
> 
> Unfortunately, a POSIX thread has a default POSIX priority of 0, which
> translates to an ECOS_PRIORITY of (CYG_THREAD_MIN_PRIORITY-priority) i.e.
> 31. Not only is this less than main's, it is the same as the idle thread,
> meaning it will be timeslicing with it.
> 
> I think instead sched_priority in pthread_attr_init() should default to 1.
> Nick, know any reason why not?
> 

It is actually irrelevant, since the inherit attribute is set to
PTHREAD_INHERIT_SCHED the default is for all threads to inherit the
priority of their creator.

Without looking at Jaiprakash's program, it is difficult to know what
is actually happening.


-- 
Nick Garnett, eCos Kernel Architect
Red Hat, Cambridge, UK

Re: [ECOS] Thread related queries

[Jonathan Larmour]

Nick Garnett wrote:
> It is actually irrelevant, since the inherit attribute is set to
> PTHREAD_INHERIT_SCHED the default is for all threads to inherit the
> priority of their creator.

True, I missed that aspect.
 
> Without looking at Jaiprakash's program, it is difficult to know what
> is actually happening.

It's here: http://sources.redhat.com/ml/ecos-discuss/2001-08/msg00846.html
but I don't see anything suspect.

Jaiprakash should try to debug it. In particular, in GDB set a breakpoint
and do "info threads" to see what the thread priorities _really_ are.

Jifl
-- 
Red Hat, Rustat House, Clifton Road, Cambridge, UK. Tel: +44 (1223) 271062
Maybe this world is another planet's Hell -Aldous Huxley || Opinions==mine