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SubjectRe: [PATCH 2/5] 2.6.0 sched fork cleanup

* Nick Piggin <piggin@cyberone.com.au> wrote:

> Move some fork related scheduler policy from fork.c to sched.c where
> it belongs.

this only makes sense if all the other fork-time initializations are
done in sched.c too - these are scattered all around copy_process().
The attached patch (it compiles & boots) does this. All the lowlevel
scheduler logic (that was done in fork.c) is now in sched.c - fork.c
only sees the higher level primitives. I've also updated a couple of
comments that relate to the affected code.

Ingo
--- linux/include/linux/sched.h.orig
+++ linux/include/linux/sched.h
@@ -580,6 +580,7 @@ extern int FASTCALL(wake_up_process(stru
static inline void kick_process(struct task_struct *tsk) { }
#endif
extern void FASTCALL(wake_up_forked_process(struct task_struct * tsk));
+extern void FASTCALL(sched_fork(task_t * p));
extern void FASTCALL(sched_exit(task_t * p));

asmlinkage long sys_wait4(pid_t pid,unsigned int * stat_addr, int options, struct rusage * ru);
--- linux/kernel/fork.c.orig
+++ linux/kernel/fork.c
@@ -876,15 +876,7 @@ struct task_struct *copy_process(unsigne
if (p->binfmt && !try_module_get(p->binfmt->module))
goto bad_fork_cleanup_put_domain;

-#ifdef CONFIG_PREEMPT
- /*
- * schedule_tail drops this_rq()->lock so we compensate with a count
- * of 1. Also, we want to start with kernel preemption disabled.
- */
- p->thread_info->preempt_count = 1;
-#endif
p->did_exec = 0;
- p->state = TASK_UNINTERRUPTIBLE;

copy_flags(clone_flags, p);
if (clone_flags & CLONE_IDLETASK)
@@ -901,15 +893,12 @@ struct task_struct *copy_process(unsigne

p->proc_dentry = NULL;

- INIT_LIST_HEAD(&p->run_list);
-
INIT_LIST_HEAD(&p->children);
INIT_LIST_HEAD(&p->sibling);
INIT_LIST_HEAD(&p->posix_timers);
init_waitqueue_head(&p->wait_chldexit);
p->vfork_done = NULL;
spin_lock_init(&p->alloc_lock);
- spin_lock_init(&p->switch_lock);
spin_lock_init(&p->proc_lock);

clear_tsk_thread_flag(p, TIF_SIGPENDING);
@@ -924,7 +913,6 @@ struct task_struct *copy_process(unsigne
p->tty_old_pgrp = 0;
p->utime = p->stime = 0;
p->cutime = p->cstime = 0;
- p->array = NULL;
p->lock_depth = -1; /* -1 = no lock */
p->start_time = get_jiffies_64();
p->security = NULL;
@@ -973,38 +961,12 @@ struct task_struct *copy_process(unsigne
p->exit_signal = (clone_flags & CLONE_THREAD) ? -1 : (clone_flags & CSIGNAL);
p->pdeath_signal = 0;

+ /* Perform scheduler related setup */
+ sched_fork(p);
+
/*
- * Share the timeslice between parent and child, thus the
- * total amount of pending timeslices in the system doesn't change,
- * resulting in more scheduling fairness.
- */
- local_irq_disable();
- p->time_slice = (current->time_slice + 1) >> 1;
- /*
- * The remainder of the first timeslice might be recovered by
- * the parent if the child exits early enough.
- */
- p->first_time_slice = 1;
- current->time_slice >>= 1;
- p->timestamp = sched_clock();
- if (!current->time_slice) {
- /*
- * This case is rare, it happens when the parent has only
- * a single jiffy left from its timeslice. Taking the
- * runqueue lock is not a problem.
- */
- current->time_slice = 1;
- preempt_disable();
- scheduler_tick(0, 0);
- local_irq_enable();
- preempt_enable();
- } else
- local_irq_enable();
- /*
- * Ok, add it to the run-queues and make it
- * visible to the rest of the system.
- *
- * Let it rip!
+ * Ok, make it visible to the rest of the system.
+ * We dont wake it up yet.
*/
p->tgid = p->pid;
p->group_leader = p;
--- linux/kernel/sched.c.orig
+++ linux/kernel/sched.c
@@ -674,6 +674,54 @@ int wake_up_state(task_t *p, unsigned in
}

/*
+ * Perform scheduler related setup for a newly forked process p.
+ * p is forked by current.
+ */
+void sched_fork(task_t *p)
+{
+ p->state = TASK_UNINTERRUPTIBLE;
+ INIT_LIST_HEAD(&p->run_list);
+ p->array = NULL;
+ spin_lock_init(&p->switch_lock);
+#ifdef CONFIG_PREEMPT
+ /*
+ * During context-switch we hold precisely one spinlock, which
+ * schedule_tail drops. (in the common case it's this_rq()->lock,
+ * but it also can be p->switch_lock.) So we compensate with a count
+ * of 1. Also, we want to start with kernel preemption disabled.
+ */
+ p->thread_info->preempt_count = 1;
+#endif
+ /*
+ * Share the timeslice between parent and child, thus the
+ * total amount of pending timeslices in the system doesn't change,
+ * resulting in more scheduling fairness.
+ */
+ local_irq_disable();
+ p->time_slice = (current->time_slice + 1) >> 1;
+ /*
+ * The remainder of the first timeslice might be recovered by
+ * the parent if the child exits early enough.
+ */
+ p->first_time_slice = 1;
+ current->time_slice >>= 1;
+ p->timestamp = sched_clock();
+ if (!current->time_slice) {
+ /*
+ * This case is rare, it happens when the parent has only
+ * a single jiffy left from its timeslice. Taking the
+ * runqueue lock is not a problem.
+ */
+ current->time_slice = 1;
+ preempt_disable();
+ scheduler_tick(0, 0);
+ local_irq_enable();
+ preempt_enable();
+ } else
+ local_irq_enable();
+}
+
+/*
* wake_up_forked_process - wake up a freshly forked process.
*
* This function will do some initial scheduler statistics housekeeping
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