Re: Linux 2.4.20-pre2

From: Bhavesh P. Davda (bhaveshd@drmail.dr.avaya.com)
Date: Tue Aug 13 2002 - 10:04:16 EST


For the Nth time, here again is the patch for fixing the scheduler for
correct SCHED_FIFO and SCHED_RR behaviour.

I waited to see it in 2.4.20-pre1, not there, 2.4.20-pre2, not there...

Please apply it in 2.4.20-pre3

Thanks

- Bhavesh

-- 
Bhavesh P. Davda
Avaya Inc.
bhavesh@avaya.com

diff -aur linux-2.4.19/kernel/sched.c linux-2.4.19-sched/kernel/sched.c --- linux-2.4.19/kernel/sched.c Tue Aug 6 11:37:49 2002 +++ linux-2.4.19-sched/kernel/sched.c Tue Aug 6 13:42:20 2002 @@ -318,13 +318,17 @@ /* * Careful! * - * This has to add the process to the _beginning_ of the - * run-queue, not the end. See the comment about "This is - * subtle" in the scheduler proper.. + * This has to add the process to the _end_ of the + * run-queue, not the beginning. The goodness value will + * determine whether this process will run next. This is + * important to get SCHED_FIFO and SCHED_RR right, where + * a process that is either pre-empted or its time slice + * has expired, should be moved to the tail of the run + * queue for its priority - Bhavesh Davda */ static inline void add_to_runqueue(struct task_struct * p) { - list_add(&p->run_list, &runqueue_head); + list_add_tail(&p->run_list, &runqueue_head); nr_running++; } @@ -334,12 +338,6 @@ list_add_tail(&p->run_list, &runqueue_head); } -static inline void move_first_runqueue(struct task_struct * p) -{ - list_del(&p->run_list); - list_add(&p->run_list, &runqueue_head); -} - /* * Wake up a process. Put it on the run-queue if it's not * already there. The "current" process is always on the @@ -955,8 +953,6 @@ retval = 0; p->policy = policy; p->rt_priority = lp.sched_priority; - if (task_on_runqueue(p)) - move_first_runqueue(p); current->need_resched = 1; diff -aur linux-2.4.19/kernel/timer.c linux-2.4.19-sched/kernel/timer.c --- linux-2.4.19/kernel/timer.c Tue Aug 6 11:37:49 2002 +++ linux-2.4.19-sched/kernel/timer.c Tue Aug 6 13:42:20 2002 @@ -601,7 +601,14 @@ if (p->pid) { if (--p->counter <= 0) { p->counter = 0; - p->need_resched = 1; + /* + * SCHED_FIFO is priority preemption, so this is + * not the place to decide whether to reschedule a + * SCHED_FIFO task or not - Bhavesh Davda + */ + if (p->policy != SCHED_FIFO) { + p->need_resched = 1; + } } if (p->nice > 0) kstat.per_cpu_nice[cpu] += user_tick;

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