[PATCH] updated O(1) scheduler for 2.4

[PATCH] updated O(1) scheduler for 2.4

[Robert Love]

Updated versions of the O(1) scheduler for 2.4 are available at:

http://www.kernel.org/pub/linux/kernel/people/rml/sched/ingo-O1/sched-O1-rml-2.4.18-4.patch
http://www.kernel.org/pub/linux/kernel/people/rml/sched/ingo-O1/sched-O1-rml-2.4.19-pre8-1.patch

for 2.4.18 and 2.4.19-pre8.  Please use a mirror.

These patches include all included and pending bits from 2.4-ac and 2.5
as well as my user-configurable maximum RT priority patch.  This is more
up-to-date than any other tree, in fact. ;-)

In general, I recommend using 2.4-ac or waiting for 2.6 if you want the
O(1) scheduler - this is not suggested for inclusion in 2.4 - but for
those who care, here it is.

Enjoy,

	Robert Love

Re: [PATCH] updated O(1) scheduler for 2.4

[J.A. Magallon]

On 2002.05.21 Robert Love wrote:
>Updated versions of the O(1) scheduler for 2.4 are available at:
>
>http://www.kernel.org/pub/linux/kernel/people/rml/sched/ingo-O1/sched-O1-rml-2.4.18-4.patch
>http://www.kernel.org/pub/linux/kernel/people/rml/sched/ingo-O1/sched-O1-rml-2.4.19-pre8-1.patch
>
>for 2.4.18 and 2.4.19-pre8.  Please use a mirror.
>
>These patches include all included and pending bits from 2.4-ac and 2.5
>as well as my user-configurable maximum RT priority patch.  This is more
>up-to-date than any other tree, in fact. ;-)
>

I had to make this to get it built:

diff -urN linux-2.4.19-pre7/init/do_mounts.c linux/init/do_mounts.c
--- linux-2.4.19-pre7/init/do_mounts.c	Sat Apr 20 20:50:36 2002
+++ linux/init/do_mounts.c	Mon Apr 22 14:18:20 2002
@@ -774,10 +774,8 @@
 
 	pid = kernel_thread(do_linuxrc, "/linuxrc", SIGCHLD);
 	if (pid > 0) {
-		while (pid != wait(&i)) {
-			current->policy |= SCHED_YIELD;
-			schedule();
-		}
+		while (pid != wait(&i))
+			yield();
 	}
 
 	sys_mount("..", ".", NULL, MS_MOVE, NULL);
diff -urN linux-2.4.19-pre7/arch/m68k/mm/fault.c linux/arch/m68k/mm/fault.c
--- linux-2.4.19-pre7/arch/m68k/mm/fault.c	Sat Apr 20 20:50:47 2002
+++ linux/arch/m68k/mm/fault.c	Mon Apr 22 14:19:29 2002
@@ -181,8 +181,7 @@
 out_of_memory:
 	up_read(&mm->mmap_sem);
 	if (current->pid == 1) {
-		current->policy |= SCHED_YIELD;
-		schedule();
+		yield();
 		down_read(&mm->mmap_sem);
 		goto survive;
 	}
diff -urN linux-2.4.19-pre7/arch/mips/mm/fault.c linux/arch/mips/mm/fault.c
--- linux-2.4.19-pre7/arch/mips/mm/fault.c	Sat Apr 20 20:50:46 2002
+++ linux/arch/mips/mm/fault.c	Mon Apr 22 14:19:15 2002
@@ -211,8 +211,7 @@
 out_of_memory:
 	up_read(&mm->mmap_sem);
 	if (tsk->pid == 1) {
-		tsk->policy |= SCHED_YIELD;
-		schedule();
+		yield();
 		down_read(&mm->mmap_sem);
 		goto survive;
 	}
diff -urN linux-2.4.19-pre7/arch/mips64/mm/fault.c linux/arch/mips64/mm/fault.c
--- linux-2.4.19-pre7/arch/mips64/mm/fault.c	Sat Apr 20 20:50:47 2002
+++ linux/arch/mips64/mm/fault.c	Mon Apr 22 14:19:55 2002
@@ -240,8 +240,7 @@
 out_of_memory:
 	up_read(&mm->mmap_sem);
 	if (tsk->pid == 1) {
-		tsk->policy |= SCHED_YIELD;
-		schedule();
+		yield();
 		down_read(&mm->mmap_sem);
 		goto survive;
 	}


and this to shut up gcc-3.1 about trying to EXPORT_ or use something undeclared:

--- linux-2.4.19-pre8-jam4/include/linux/sched.h.orig	2002-05-24 16:56:16.000000000 +0200
+++ linux-2.4.19-pre8-jam4/include/linux/sched.h	2002-05-24 17:02:12.000000000 +0200
@@ -644,6 +644,8 @@
 extern void FASTCALL(interruptible_sleep_on(wait_queue_head_t *q));
 extern long FASTCALL(interruptible_sleep_on_timeout(wait_queue_head_t *q,
 						    signed long timeout));
+extern int FASTCALL(wake_up_process(task_t * p));
+extern void FASTCALL(wake_up_forked_process(task_t * p));
 
 #define wake_up(x)			__wake_up((x),TASK_UNINTERRUPTIBLE | TASK_INTERRUPTIBLE, 1)
 #define wake_up_nr(x, nr)		__wake_up((x),TASK_UNINTERRUPTIBLE | TASK_INTERRUPTIBLE, nr)


-- 
J.A. Magallon                           #  Let the source be with you...        
mailto:jamagallon@able.es
Mandrake Linux release 8.3 (Cooker) for i586
Linux werewolf 2.4.19-pre8-jam4 #4 SMP vie may 24 17:02:32 CEST 2002 i686

Re: [PATCH] updated O(1) scheduler for 2.4

[Robert Love]

On Fri, 2002-05-24 at 09:02, J.A. Magallon wrote:

> I had to make this to get it built:
> <snip>

Thanks, I have put these changes into the 2.4.19-pre9 version of the
patch which is available at:

	http://www.kernel.org/pub/linux/kernel/people/rml/sched/ingo-O1/sched-O1-rml-2.4.19-pre9-1.patch

Hopefully Alan will put out a 2.4.19-pre9-ac1 with the last of the bits
I pushed him.

	Robert Love

Re: [PATCH] updated O(1) scheduler for 2.4

[Andrea Arcangeli]

On Tue, May 28, 2002 at 07:57:00PM -0700, Robert Love wrote:
> On Fri, 2002-05-24 at 09:02, J.A. Magallon wrote:
> 
> > I had to make this to get it built:
> > <snip>
> 
> Thanks, I have put these changes into the 2.4.19-pre9 version of the
> patch which is available at:
> 
> 	http://www.kernel.org/pub/linux/kernel/people/rml/sched/ingo-O1/sched-O1-rml-2.4.19-pre9-1.patch

I merged it and I've almost finished moving everything on top of it but
I've a few issues.

can you elaborate why you __save_flags in do_fork? do_fork is even a
blocking operation. fork_by_hand runs as well with irq enabled.
I don't like to safe flags in a fast path if it's not required.

Then there are longstanding bugs that aren't yet fixed and I ported the
fixed on top of it (see the parent-timeslice patch in -aa).

the child-run first approch in o1 is suspect, it seems the parent will
keep running just after a wasteful reschedule, a sched yield instead
should be invoked like in -aa in the share-timeslice patch in order to
roll the current->run_list before the schedule is invoked while
returning to userspace after fork.

another suspect thing I noticed is the wmb() in resched_task. Can you
elaborate on what is it trying to serialize (I hope not the read of
p->need_resched with the stuff below)? Also if something it should be a
smp_wmb(), same smp_ prefix goes for the other mb() in schedule.

thanks,

Andrea

Re: [PATCH] updated O(1) scheduler for 2.4

[Robert Love]

On Wed, 2002-05-29 at 08:15, Andrea Arcangeli wrote:

> I merged it and I've almost finished moving everything on top of it but
> I've a few issues.
> 
> can you elaborate why you __save_flags in do_fork? do_fork is even a
> blocking operation. fork_by_hand runs as well with irq enabled.
> I don't like to safe flags in a fast path if it's not required.

s/you/Ingo/ ;)

We save flags for two reasons: First, we touch task->time_slice which is
touched from an interrupt handler (timer/idle/scheduler_tick) and second
because we may call scheduler_tick which must be called with interrupts
off.  Note we restore them just a few lines later...

Or, hm, are you asking why not just cli/sti?  I don't know the answer to
that... I would think we always enter do_fork with interrupts enabled,
but maybe Ingo thought otherwise.

> Then there are longstanding bugs that aren't yet fixed and I ported the
> fixed on top of it (see the parent-timeslice patch in -aa).
> 
> the child-run first approch in o1 is suspect, it seems the parent will
> keep running just after a wasteful reschedule, a sched yield instead
> should be invoked like in -aa in the share-timeslice patch in order to
> roll the current->run_list before the schedule is invoked while
> returning to userspace after fork.

I do not see this...

> another suspect thing I noticed is the wmb() in resched_task. Can you
> elaborate on what is it trying to serialize (I hope not the read of
> p->need_resched with the stuff below)? Also if something it should be a
> smp_wmb(), same smp_ prefix goes for the other mb() in schedule.

I suspect you may be right here.  I believe the wmb() is to serialize
the reading of need_resched vs the writing of need_resched below it vs
whatever may happen to need_resched elsewhere.

But resched_task is the only bit from 2.5 I have not fully back
ported...take a look at resched_task in 2.5: I need to bring that to
2.4.  I suspect idle polling is broken in 2.4, too.

> thanks,

You are welcome ;)

	Robert Love

Re: [PATCH] updated O(1) scheduler for 2.4

[Andrea Arcangeli]

On Wed, May 29, 2002 at 11:03:14AM -0700, Robert Love wrote:
> On Wed, 2002-05-29 at 08:15, Andrea Arcangeli wrote:
> 
> > I merged it and I've almost finished moving everything on top of it but
> > I've a few issues.
> > 
> > can you elaborate why you __save_flags in do_fork? do_fork is even a
> > blocking operation. fork_by_hand runs as well with irq enabled.
> > I don't like to safe flags in a fast path if it's not required.
> 
> s/you/Ingo/ ;)
> 
> We save flags for two reasons: First, we touch task->time_slice which is
> touched from an interrupt handler (timer/idle/scheduler_tick) and second
> because we may call scheduler_tick which must be called with interrupts
> off.  Note we restore them just a few lines later...
> 
> Or, hm, are you asking why not just cli/sti?  I don't know the answer to

of course, I'm asking why not cli/sti, see my current status of
incrmental fixes on top of the o1 scheduler, some old in -aa, some from
-ac (I dropped an optimization from you, I assume it's ok but quite
frankly I don't care about the performance of setting the cpu affinity
and I preferred to stay safe in sync with -ac and 2.5), some new noticed
while mering (and still uncertain about the questions). also the
force_cpu_reschedule from the 2.5 rcu-poll was buggy and that's fixed
too now in my tree.

beware I cannot test anything yet, the tree still doesn't compile, it seems
the last thing to make uml link is to update the init_task, then I will
also need to do the same for x86-64 at least, and possibly other archs
if Robert didn't took care of them. after x86-64 and uml works I will
check sparc64 alpha and finally x86 smp + up.

diff -urNp o1-sched-ref/include/linux/wait.h o1-sched/include/linux/wait.h
--- o1-sched-ref/include/linux/wait.h	Wed May 29 19:58:06 2002
+++ o1-sched/include/linux/wait.h	Wed May 29 20:17:12 2002
@@ -59,6 +59,7 @@ typedef struct __wait_queue wait_queue_t
 # define wq_write_lock_irq write_lock_irq
 # define wq_write_lock_irqsave write_lock_irqsave
 # define wq_write_unlock_irqrestore write_unlock_irqrestore
+# define wq_write_unlock_irq write_unlock_irq
 # define wq_write_unlock write_unlock
 #else
 # define wq_lock_t spinlock_t
@@ -71,6 +72,7 @@ typedef struct __wait_queue wait_queue_t
 # define wq_write_lock_irq spin_lock_irq
 # define wq_write_lock_irqsave spin_lock_irqsave
 # define wq_write_unlock_irqrestore spin_unlock_irqrestore
+# define wq_write_unlock_irq spin_unlock_irq
 # define wq_write_unlock spin_unlock
 #endif
 
diff -urNp o1-sched-ref/kernel/sched.c o1-sched/kernel/sched.c
--- o1-sched-ref/kernel/sched.c	Wed May 29 20:16:59 2002
+++ o1-sched/kernel/sched.c	Wed May 29 20:17:07 2002
@@ -850,15 +850,15 @@ void complete(struct completion *x)
 {
 	unsigned long flags;
 
-	spin_lock_irqsave(&x->wait.lock, flags);
+	wq_write_lock_irqsave(&x->wait.lock, flags);
 	x->done++;
 	__wake_up_common(&x->wait, TASK_UNINTERRUPTIBLE | TASK_INTERRUPTIBLE, 1);
-	spin_unlock_irqrestore(&x->wait.lock, flags);
+	wq_write_unlock_irqrestore(&x->wait.lock, flags);
 }
 
 void wait_for_completion(struct completion *x)
 {
-	spin_lock_irq(&x->wait.lock);
+	wq_write_lock_irq(&x->wait.lock);
 	if (!x->done) {
 		DECLARE_WAITQUEUE(wait, current);
 
@@ -866,14 +866,14 @@ void wait_for_completion(struct completi
 		__add_wait_queue_tail(&x->wait, &wait);
 		do {
 			__set_current_state(TASK_UNINTERRUPTIBLE);
-			spin_unlock_irq(&x->wait.lock);
+			wq_write_unlock_irq(&x->wait.lock);
 			schedule();
-			spin_lock_irq(&x->wait.lock);
+			wq_write_lock_irq(&x->wait.lock);
 		} while (!x->done);
 		__remove_wait_queue(&x->wait, &wait);
 	}
 	x->done--;
-	spin_unlock_irq(&x->wait.lock);
+	wq_write_unlock_irq(&x->wait.lock);
 }
 
 #define	SLEEP_ON_VAR				\
@@ -1499,8 +1499,8 @@ typedef struct {
  * is removed from the allowed bitmask.
  *
  * NOTE: the caller must have a valid reference to the task, the
- * task must not exit() & deallocate itself prematurely.  The
- * call is not atomic; no spinlocks may be held.
+ * task must not exit() & deallocate itself prematurely.  No
+ * spinlocks can be held.
  */
 void set_cpus_allowed(task_t *p, unsigned long new_mask)
 {
@@ -1523,16 +1523,6 @@ void set_cpus_allowed(task_t *p, unsigne
 		return;
 	}
 
-	/*
-	 * If the task is not on a runqueue, then it is safe to
-	 * simply update the task's cpu field.
-	 */
-	if (!p->array) {
-		p->cpu = __ffs(p->cpus_allowed);
-		task_rq_unlock(rq, &flags);
-		return;
-	}
-
 	init_MUTEX_LOCKED(&req.sem);
 	req.task = p;
 	list_add(&req.list, &rq->migration_queue);


--- ./kernel/sched.c.~1~	Wed May 29 04:50:30 2002
+++ ./kernel/sched.c	Wed May 29 05:22:04 2002
@@ -569,7 +569,7 @@ skip_queue:
 #define CAN_MIGRATE_TASK(p,rq,this_cpu)					\
 	((jiffies - (p)->sleep_timestamp > cache_decay_ticks) &&	\
 		((p) != (rq)->curr) &&					\
-			((p)->cpus_allowed & (1 << (this_cpu))))
+			((p)->cpus_allowed & (1UL << (this_cpu))))
 
 	if (!CAN_MIGRATE_TASK(tmp, busiest, this_cpu)) {
 		curr = curr->next;



--- sched2/kernel/sched.c.~1~	Wed May 29 17:24:52 2002
+++ sched2/kernel/sched.c	Wed May 29 17:34:22 2002
@@ -248,7 +248,6 @@ static inline void resched_task(task_t *
 	int need_resched;
 
 	need_resched = p->need_resched;
-	wmb();
 	set_tsk_need_resched(p);
 	if (!need_resched && (p->cpu != smp_processor_id()))
 		smp_send_reschedule(p->cpu);
@@ -794,7 +793,7 @@ switch_tasks:
 		 * if the new task was last running on a different
 		 * CPU - thus re-load it.
 		 */
-		mb();
+		smp_mb();
 		rq = this_rq();
 		spin_unlock_irq(&rq->frozen);
 	} else {
--- sched2/kernel/fork.c.~1~	Wed May 29 17:24:52 2002
+++ sched2/kernel/fork.c	Wed May 29 17:34:39 2002
@@ -712,7 +712,6 @@ int do_fork(unsigned long clone_flags, u
 	 * total amount of pending timeslices in the system doesnt change,
 	 * resulting in more scheduling fairness.
 	 */
-	__save_flags(flags);
 	__cli();
 	if (!current->time_slice)
 		BUG();
@@ -728,7 +727,7 @@ int do_fork(unsigned long clone_flags, u
 		scheduler_tick(0,0);
 	}
 	p->sleep_timestamp = jiffies;
-	__restore_flags(flags);
+	__sti();
 
 	/*
 	 * Ok, add it to the run-queues and make it


diff -urNp o1-sched-ref/include/linux/sched.h o1-sched/include/linux/sched.h
--- o1-sched-ref/include/linux/sched.h	Wed May 29 17:36:11 2002
+++ o1-sched/include/linux/sched.h	Wed May 29 17:36:32 2002
@@ -371,6 +371,7 @@ struct task_struct {
 	unsigned long policy;
 	unsigned long cpus_allowed;
 	unsigned int time_slice;
+	int get_child_timeslice;
 
 	task_t *next_task, *prev_task;
 
diff -urNp o1-sched-ref/kernel/exit.c o1-sched/kernel/exit.c
--- o1-sched-ref/kernel/exit.c	Wed May 29 17:36:10 2002
+++ o1-sched/kernel/exit.c	Wed May 29 17:36:32 2002
@@ -231,6 +231,7 @@ static inline void forget_original_paren
 			else
 				p->p_opptr = reaper;
 
+			p->get_child_timeslice = 0;
 			if (p->pdeath_signal) send_sig(p->pdeath_signal, p, 0);
 		}
 	}
diff -urNp o1-sched-ref/kernel/fork.c o1-sched/kernel/fork.c
--- o1-sched-ref/kernel/fork.c	Wed May 29 17:36:21 2002
+++ o1-sched/kernel/fork.c	Wed May 29 17:36:49 2002
@@ -729,6 +729,8 @@ int do_fork(unsigned long clone_flags, u
 	}
 	p->sleep_timestamp = jiffies;
 	__sti();
+	/* Tell the parent if it can get back its timeslice when child exits */
+	p->get_child_timeslice = 1;
 
 	/*
 	 * Ok, add it to the run-queues and make it
diff -urNp o1-sched-ref/kernel/sched.c o1-sched/kernel/sched.c
--- o1-sched-ref/kernel/sched.c	Wed May 29 17:36:21 2002
+++ o1-sched/kernel/sched.c	Wed May 29 17:36:32 2002
@@ -360,9 +360,11 @@ void wake_up_forked_process(task_t * p)
 void sched_exit(task_t * p)
 {
 	__cli();
-	current->time_slice += p->time_slice;
-	if (unlikely(current->time_slice > MAX_TIMESLICE))
-		current->time_slice = MAX_TIMESLICE;
+	if (p->get_child_timeslice) {
+		current->time_slice += p->time_slice;
+		if (unlikely(current->time_slice > MAX_TIMESLICE))
+			current->time_slice = MAX_TIMESLICE;
+	}
 	__sti();
 	/*
 	 * If the child was a (relative-) CPU hog then decrease
@@ -673,6 +675,7 @@ void scheduler_tick(int user_tick, int s
 		 */
 		if ((p->policy == SCHED_RR) && !--p->time_slice) {
 			p->time_slice = TASK_TIMESLICE(p);
+			p->get_child_timeslice = 0;
 			set_tsk_need_resched(p);
 
 			/* put it at the end of the queue: */
@@ -696,6 +699,7 @@ void scheduler_tick(int user_tick, int s
 		set_tsk_need_resched(p);
 		p->prio = effective_prio(p);
 		p->time_slice = TASK_TIMESLICE(p);
+		p->get_child_timeslice = 0;
 
 		if (!TASK_INTERACTIVE(p) || EXPIRED_STARVING(rq)) {
 			if (!rq->expired_timestamp)


diff -urNp o1-sched/include/linux/sched.h o1-sched-child-first/include/linux/sched.h
--- o1-sched/include/linux/sched.h	Wed May 29 17:36:32 2002
+++ o1-sched-child-first/include/linux/sched.h	Wed May 29 17:40:12 2002
@@ -509,6 +509,7 @@ extern void set_user_nice(task_t *p, lon
 extern int task_prio(task_t *p);
 extern int task_nice(task_t *p);
 
+extern void __sched_yield(void);
 asmlinkage long sys_sched_yield(void);
 #define yield()	sys_sched_yield()
 
diff -urNp o1-sched/kernel/fork.c o1-sched-child-first/kernel/fork.c
--- o1-sched/kernel/fork.c	Wed May 29 17:42:11 2002
+++ o1-sched-child-first/kernel/fork.c	Wed May 29 17:40:47 2002
@@ -770,12 +770,14 @@ int do_fork(unsigned long clone_flags, u
 	++total_forks;
 	if (clone_flags & CLONE_VFORK)
 		wait_for_completion(&vfork);
-	else
+	else {
 		/*
 		 * Let the child process run first, to avoid most of the
 		 * COW overhead when the child exec()s afterwards.
 		 */
+		__sched_yield();
 		current->need_resched = 1;
+	}
 
 fork_out:
 	return retval;
diff -urNp o1-sched/kernel/sched.c o1-sched-child-first/kernel/sched.c
--- o1-sched/kernel/sched.c	Wed May 29 17:36:32 2002
+++ o1-sched-child-first/kernel/sched.c	Wed May 29 17:39:57 2002
@@ -1182,7 +1182,7 @@ out_unlock:
 	return retval;
 }
 
-asmlinkage long sys_sched_yield(void)
+void __sched_yield(void)
 {
 	runqueue_t *rq;
 	prio_array_t *array;
@@ -1215,6 +1215,11 @@ asmlinkage long sys_sched_yield(void)
 		__set_bit(current->prio, array->bitmap);
 	}
 	spin_unlock(&rq->lock);
+}
+
+asmlinkage long sys_sched_yield(void)
+{
+	__sched_yield();
 
 	schedule();
 

> that... I would think we always enter do_fork with interrupts enabled,
> but maybe Ingo thought otherwise.
> 
> > Then there are longstanding bugs that aren't yet fixed and I ported the
> > fixed on top of it (see the parent-timeslice patch in -aa).
> > 
> > the child-run first approch in o1 is suspect, it seems the parent will
> > keep running just after a wasteful reschedule, a sched yield instead
> > should be invoked like in -aa in the share-timeslice patch in order to
> > roll the current->run_list before the schedule is invoked while
> > returning to userspace after fork.
> 
> I do not see this...

see the above serie of patches, again it may be broken, still untested yet.

> > another suspect thing I noticed is the wmb() in resched_task. Can you
> > elaborate on what is it trying to serialize (I hope not the read of
> > p->need_resched with the stuff below)? Also if something it should be a
> > smp_wmb(), same smp_ prefix goes for the other mb() in schedule.
> 
> I suspect you may be right here.  I believe the wmb() is to serialize
> the reading of need_resched vs the writing of need_resched below it vs
> whatever may happen to need_resched elsewhere.

I actually removed it enterely, need_resched will be fore sure read
before overwriting it because it's guaranteed by reading and writing to
the same mem address.

still I wonder if the other cpu will see the need_resched set when it
goes to read it, I can imagine a needed wmb() on the writer cpu and an rmb() in
the reader, hopefully it serializes via the spinlocks, I didn't touch
this area, but if the wmb() was meant to be after need_resced = 1, that
had to be one line below, so still it would be a bug, the wmb() in such
place looks superflous so I dropped it until somebody comments.

> 
> But resched_task is the only bit from 2.5 I have not fully back
> ported...take a look at resched_task in 2.5: I need to bring that to
> 2.4.  I suspect idle polling is broken in 2.4, too.

your version looks ok at first glance.

Andrea

Re: [PATCH] updated O(1) scheduler for 2.4

[Robert Love]

On Wed, 2002-05-29 at 12:13, Andrea Arcangeli wrote:

> of course, I'm asking why not cli/sti, see my current status of
> incrmental fixes on top of the o1 scheduler, some old in -aa, some from
> -ac

Right.  I suspect Ingo knew something, otherwise he would not of used
the save/restore variant... but it is good to remove it if we can.

> (I dropped an optimization from you, I assume it's ok but quite
> frankly I don't care about the performance of setting the cpu affinity
> and I preferred to stay safe in sync with -ac and 2.5),

Well, that optimize is not just for benefiting the affinity syscalls but
any caller of set_cpus_allowed ... but OK.  However, it is now in 2.5.19
and should be in 2.4.19-pre9-ac1 as I pushed it to Alan.

> some new noticed
> while mering (and still uncertain about the questions). also the
> force_cpu_reschedule from the 2.5 rcu-poll was buggy and that's fixed
> too now in my tree.
> 
> beware I cannot test anything yet, the tree still doesn't compile, it seems
> the last thing to make uml link is to update the init_task, then I will
> also need to do the same for x86-64 at least, and possibly other archs
> if Robert didn't took care of them. after x86-64 and uml works I will
> check sparc64 alpha and finally x86 smp + up.

There are missing bits from non-x86 architectures.  I am going to get to
that next but as I only have x86 it will be slow.  I suspect it is very
easy, however - just grabbing the bitop instructions from include/asm. 
I deliberately did not backport any changes that had significant
arch-specific ramifications.

> --- ./kernel/sched.c.~1~	Wed May 29 04:50:30 2002
> +++ ./kernel/sched.c	Wed May 29 05:22:04 2002
> @@ -569,7 +569,7 @@ skip_queue:
>  #define CAN_MIGRATE_TASK(p,rq,this_cpu)					\
>  	((jiffies - (p)->sleep_timestamp > cache_decay_ticks) &&	\
>  		((p) != (rq)->curr) &&					\
> -			((p)->cpus_allowed & (1 << (this_cpu))))
> +			((p)->cpus_allowed & (1UL << (this_cpu))))
>  
>  	if (!CAN_MIGRATE_TASK(tmp, busiest, this_cpu)) {
>  		curr = curr->next;

Ahh, good eye...

> see the above serie of patches, again it may be broken, still untested yet.

I need to look into your patches and the current behavior, as I do not
see anything broken with the current implementation.

> I actually removed it enterely, need_resched will be fore sure read
> before overwriting it because it's guaranteed by reading and writing to
> the same mem address.
> 
> still I wonder if the other cpu will see the need_resched set when it
> goes to read it, I can imagine a needed wmb() on the writer cpu and an rmb() in
> the reader, hopefully it serializes via the spinlocks, I didn't touch
> this area, but if the wmb() was meant to be after need_resced = 1, that
> had to be one line below, so still it would be a bug, the wmb() in such
> place looks superflous so I dropped it until somebody comments.

Best to ask Ingo his intentions here.

> > But resched_task is the only bit from 2.5 I have not fully back
> > ported...take a look at resched_task in 2.5: I need to bring that to
> > 2.4.  I suspect idle polling is broken in 2.4, too.
> 
> your version looks ok at first glance.

Regards,

	Robert Love