allowed_cpus. If an idle task is running in task->processor (best_cpu) and if

need_resched is not set to -1,and if this_cpu (current->processor) is not

equal to best_cpu,it sends a reschedule event to that cpu.(smp_send_reschedule).

If an idle_task is not running,then it loops through the list of processors,and

tries to find an idle_task which has not run for the maximum time,or tries to

locate a task with a positive maximum pre-emption goodness if it fails in

getting an idle task on all cpus,before sending a reschedule event on that cpu.

The goodness routine which tries to find the goodness value is pretty simple.It

masks out SCHED_YIELD with a negative return,real_time tasks with SCHED_FIFO and

SCHED_RR policies are given the maximum increment of +1000 on a

task->rt_priority.The SCHED_OTHER guys,get their time_slices added with their

NICE value. (-20 highest to +19 lowest.) There are also many helper functions

defined in sched.c which might be of interest. wake_ups aside,schedule_timeout

is one such function which uses Kernel Timers (check it out for timer_list

usage., to schedule out a task,and bring it back into action. (see

include/linux/timer.h.) Kernel Timers can be used when one wants to run a

tasklet at a defined time in future. You can set the expiry interval of the

timer in jiffies (number of clock_ticks since System Boot, and is incremented HZ

(include/linux/param.h) times/SEC.

{

struct timer_list your_timer;

init_timer(&your_timer);

your_timer.expires = jiffies + HZ * 5;

your_timer.function = your_function;

your_timer.data = (unsigned long)current;

add_timer(&your_timer); /*It gets called after 5 secs,which is set as the

expiry of the timer. */

}

Signal Handling :

In order to get inside signal_handling,one should focus on

kernel/signal.c,and arch/i386/kernel/signal.c. Also look up the headers in

include/{asm,linux}/{sigcontext.h,siginfo.h,signal.h} for the data_structures.

Each signal has a stack frame. Thats setup in set_sigcontext

(arch/i386/kernel/signal.c), by storing the stack of the user at the time of

ret_from_sys_call(a.k.a struct pt_regs,include/asm/ptrace.h), in the sigcontext

structure. This way,it performs a magic to switch to signal handler,by setting

up the stack context to the sigframe. Try analysing the sigframe structure which