What is 2.6 Kernel's max concurrent threads?

Heya,

We've been struggling with ways to get more concurrent threads on our RedHat boxes for months now. Redhat defaults to 255 threads and then stops there. Slackware defaults to 1500 out of the box which is a lot better. Supposedly, with tweaking and recompiling glibc, you can attain up to 4096 or 8192 threads. All of our attempts at this failed! Then, someone told me that the 2.6 kernel uses a new threading model that doesn't rely on glibc. Does anyone know more about this?

How many concurrent threads can you achieve with Kernel 2.6 ?

/*
 * This controls the default maximum pid allocated to a process
 */
#define PID_MAX_DEFAULT 0x8000

/*
 * A maximum of 4 million PIDs should be enough for a while:
 */
#define PID_MAX_LIMIT (4*1024*1024)

I did find the above in threads.h from the 2.6.4 kernel source.

This would seam to show that 32768 is the max pid's for a process and that 4 million or so is the max for the machine.

Not knowing exactly how it is all glued together in the threading system I can't tell you if these actually mean what I think they might mean.

Originally posted by jtshaw *snip* I did find the above in threads.h from the 2.6.4 kernel source. This would seam to show that 32768 is the max pid's for a process and that 4 million or so is the max for the machine. Not knowing exactly how it is all glued together in the threading system I can't tell you if these actually mean what I think they might mean.

Thanks jtshaw,

that's promising... Has anyone run a thread testing app with the 2.6 kernel?
Or does anyone have any concrete info on how many concurrent threads are
possible with 2.6 ?

thanks,
meeble

hermm, I ran this bit of code

#include <stdio.h>
#include <stdlib.h>
#include <pthread.h>

int cnt_created_threads=0;

void* thrd(void *dmy){
   cnt_created_threads++;
   pthread_exit(NULL);
}

int main(int argc, char* argv[]){
   int i=0;
   int thread_handle=0;
   pthread_t th_dummy;

   for(i=0;i<100000;i++){
      thread_handle=pthread_create(&th_dummy,NULL,&thrd,NULL);
      printf("cnt_created_threads=%d,i=%d\n",cnt_created_threads,i);
   }

   return EXIT_SUCCESS;
}

On my 2.6.4 kernel machine and it only got up to 255.........

I'll see if I can change that number somehow.

EDIT:
And yes.. oddly enough, I compile/run it on my slackware server and it goes up to 1532

Originally posted by jtshaw hermm, I ran this bit of code On my 2.6.4 kernel machine and it only got up to 255......... I'll see if I can change that number somehow. EDIT: And yes.. oddly enough, I compile/run it on my slackware server and it goes up to 1532

weird. so, the exact same 2.6.4 kernel on slackware gets 1532 threads where it only got 255 on RedHat? I wonder if glibc is compiled differently on slackware...

I e-mailed Patrick over at Slackware and asked him if he knew what caused that behavior. If I hear back from him I'll let you know.

Originally posted by jtshaw I e-mailed Patrick over at Slackware and asked him if he knew what caused that behavior. If I hear back from him I'll let you know.

thanks...