linux-kernel - QUESTION: RT & SCHED & fork: ?MISSING EQUIV of task_new

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Date:	Tue, 14 Aug 2007 12:28:02 -0700
From:	"Mitchell Erblich" <erblichs@...thlink.net>
To:	"\"Linux Kernel Mailing List\"" <linux-kernel@...r.kernel.org>
Cc:	"\"Ingo Molnar\"" <mingo@...e.hu>,
	"\"\\\"Dmitry Adamushko\\\"\"" <dmitry.adamushko@...il.com>
Subject: QUESTION: RT & SCHED & fork: ?MISSING EQUIV of task_new_fair for RT tasks.

Group, Ingo Molnar, etc,

Why does the rt sched_class contain fewer elements than fair?
missing is the RT for .task_new.

called by do_fork(): fork.c , which calls wake_up_new_task() via
if (!(clone_flags & CLONE_STOPPED))
      wake_up_new_task(p, clone_flags);

which is in sched.c and calls
if (!p->sched_class->task_new ||

       and
 p->sched_class->task_new(rq, p, now);


sched_rt.c:
static struct sched_class rt_sched_class __read_mostly = {
217         .enqueue_task           = enqueue_task_rt,
218         .dequeue_task           = dequeue_task_rt,
219         .yield_task             = yield_task_rt,
220 
221         .check_preempt_curr     = check_preempt_curr_rt,
222 
223         .pick_next_task         = pick_next_task_rt,
224         .put_prev_task          = put_prev_task_rt,
225 
226         .load_balance           = load_balance_rt,
227 
228         .task_tick              = task_tick_rt,
229 };


sched_fair.c:
struct sched_class fair_sched_class __read_mostly = {
1075         .enqueue_task           = enqueue_task_fair,
1076         .dequeue_task           = dequeue_task_fair,
1077         .yield_task             = yield_task_fair,
1078 
1079         .check_preempt_curr     = check_preempt_curr_fair,
1080 
1081         .pick_next_task         = pick_next_task_fair,
1082         .put_prev_task          = put_prev_task_fair,
1083 
1084         .load_balance           = load_balance_fair,
1085 
1086         .set_curr_task          = set_curr_task_fair,
1087         .task_tick              = task_tick_fair,
1088         .task_new               = task_new_fair,
1089 };
1090 

The missing rt equivalent item is:
/*
1014  * Share the fairness runtime between parent and child, thus the
1015  * total amount of pressure for CPU stays equal - new tasks
1016  * get a chance to run but frequent forkers are not allowed to
1017  * monopolize the CPU. Note: the parent runqueue is locked,
1018  * the child is not running yet.
1019  */
1020 static void task_new_fair(struct rq *rq, struct task_struct *p)
1021 {

Mitchell Erblich

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