RE: A question about sceduling

[Zhang, Yanmin]

>>-----Original Message-----
>>From: linux-kernel-owner@xxxxxxxxxxxxxxx
>>[mailto:linux-kernel-owner@xxxxxxxxxxxxxxx] On Behalf Of Roy Lee
>>Sent: 2005年9月16日 15:16
>>To: linux-kernel@xxxxxxxxxxxxxxx
>>Subject: A question about sceduling
>>
>>I'm tracing the scheduling code of 2.6.12.
>>During the process creation, the parent process would let the child process
>>execute first to avoid the COW overhead.
>>
>>In wake_up_new_task():
>>
>>                   if (!(clone_flags & CLONE_VM)) {
>>            /*
>>             * The VM isn't cloned, so we're in a good position to
>>             * do child-runs-first in anticipation of an exec. This
>>             * usually avoids a lot of COW overhead.
>>             */
>>            if (unlikely(!current->array))
>>                __activate_task(p, rq);
>>            else {
>>                p->prio = current->prio;
>>                list_add_tail(&p->run_list, &current->run_list);
>>                p->array = current->array;
>>                p->array->nr_active++;
>>                rq->nr_running++;
>>            }
>>            set_need_resched();
>>
>>It sets the flag to notify the kernel to reschedule.
>>But, the child has the same priority as it's parent and is the at the "tail"
>>of that priority queue.
list_add_tail(&p->run_list, &current->run_list) means insert the child into run list before parent (current)., not the tail of that priority queue.

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