Creating random seed different for different processors

tsakunthala · 01-05-2007, 10:46 AM

I need to create random numbers within specific range but different for different processors..Is that possible in C? for example when i call random function to select numbers within 10...calling this thrice i may get 0,4,7 on Processor1 and 3,5,9 on another processor..

jim mcnamara · 01-05-2007, 11:33 AM

First off: you have a bad assumption. Processor affinity in Linux is set to be "let this process use all CPU's". This means that the process will bounce around from CPU to CPU - it is not required not stay on just one CPU for the lifetime of the process.

sched_set_affinity() can be used to alter the bitmap in the task_struct's cpus_allowed bitmask - force the process to run on just one cpu.

Once you know which processor number to use, you can call some thing like this to seed the PNRG: Don't know whether you are using rand() or not, this uses srand. Pass it the cpu number you selected.

Code:

#include <stdlib.h>
#include <time.h>

int foo(const long processor_number)
{
	struct timeval seed;
	struct timezone tzp;
	int retval=0;
	
	if(!gettimeofday (&seed, &tzp))
	{
		srand(seed.tv_usec/processor_number);
		retval=1;
	}   
	return retval;
 }