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Date: Thu, 6 Mar 2003 07:58:12 +0100 (CET)
From: Ingo Molnar <mingo@elte.hu>
Reply-To: Ingo Molnar <mingo@elte.hu>
To: Andrew Morton <akpm@digeo.com>
Cc: Robert Love <rml@tech9.net>, <linux-kernel@vger.kernel.org>,
       Linus Torvalds <torvalds@transmeta.com>
Subject: [patch] "interactivity changes", sched-2.5.64-A4
In-Reply-To: <20030228202555.4391bf87.akpm@digeo.com>
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Andrew,

> hm, you're right.  It's still really bad.  I forgot that I was using
> distcc.
> 
> And I also forgot that tbench starves everything else only on
> CONFIG_SMP=n. That problem remains with us as well.

well, i took out the interactivity improvements from the 2.5.59-E6
scheduler patch, to keep the pure HT-scheduler bits only, and havent added
them back since. The two patch-sets (interactivity, and HT scheduler)
interact heavily, so i did not post the patch separately, but here it goes
as-is, against 2.5.64 - does it help your interactivity problems on UP
setups?

The patch includes the following items:

 - a new wakeup feature: SMART_WAKE_CHILD (default:1) [this is a reworked 
   version of the wakeup changes from Andrea's tree.]

 - scheduler parameter tunings (CHILD_PENALTY, MAX_TIMESLICE,
   STARVATION_LIMIT, MAX_SLEEP_AVG)

 - activate_task() splitup to separate the interactivity-active variant 
   from the task-queue variant => this fixes our statistics in some cases.

 - finer-grained preemption: if priority is equal then the task with the 
   longer pending timeslice wins.

 - make it possible to disable sync-wakeups via SYNC_WAKEUPS (default:1)

 - a naming cleanup (sleep_timestamp => last_run)

 - fix up STARVATION_LIMIT usage so that a value of 0 is recognized as 'no
   starvation limit'.

ideally we'd like to have these piece by piece, but could you just give
this patchset a go, and if it makes a difference then we can separate out
the bits that matter, to pinpoint your problems as exactly as possible.

i've test-booted the patch on UP and SMP as well.

	Ingo

--- linux/include/linux/sched.h.orig	
+++ linux/include/linux/sched.h	
@@ -328,7 +328,7 @@ struct task_struct {
 	prio_array_t *array;
 
 	unsigned long sleep_avg;
-	unsigned long sleep_timestamp;
+	unsigned long last_run;
 
 	unsigned long policy;
 	unsigned long cpus_allowed;
--- linux/kernel/sched.c.orig	
+++ linux/kernel/sched.c	
@@ -54,20 +54,21 @@
 /*
  * These are the 'tuning knobs' of the scheduler:
  *
- * Minimum timeslice is 10 msecs, default timeslice is 150 msecs,
- * maximum timeslice is 300 msecs. Timeslices get refilled after
+ * Minimum timeslice is 10 msecs, default timeslice is 100 msecs,
+ * maximum timeslice is 200 msecs. Timeslices get refilled after
  * they expire.
  */
 #define MIN_TIMESLICE		( 10 * HZ / 1000)
-#define MAX_TIMESLICE		(300 * HZ / 1000)
-#define CHILD_PENALTY		95
+#define MAX_TIMESLICE		(200 * HZ / 1000)
+#define CHILD_PENALTY		50
 #define PARENT_PENALTY		100
 #define EXIT_WEIGHT		3
 #define PRIO_BONUS_RATIO	25
 #define INTERACTIVE_DELTA	2
-#define MAX_SLEEP_AVG		(2*HZ)
-#define STARVATION_LIMIT	(2*HZ)
-#define NODE_THRESHOLD          125
+#define MAX_SLEEP_AVG		(10*HZ)
+#define STARVATION_LIMIT	(10*HZ)
+#define SYNC_WAKEUPS		1
+#define SMART_WAKE_CHILD	1
 
 /*
  * If a task is 'interactive' then we reinsert it in the active
@@ -323,16 +324,21 @@ static inline int effective_prio(task_t 
  * Also update all the scheduling statistics stuff. (sleep average
  * calculation, priority modifiers, etc.)
  */
+static inline void __activate_task(task_t *p, runqueue_t *rq)
+{
+	enqueue_task(p, rq->active);
+	rq->nr_running++;
+}
+
 static inline void activate_task(task_t *p, runqueue_t *rq)
 {
-	unsigned long sleep_time = jiffies - p->sleep_timestamp;
-	prio_array_t *array = rq->active;
+	unsigned long sleep_time = jiffies - p->last_run;
 
 	if (!rt_task(p) && sleep_time) {
 		/*
 		 * This code gives a bonus to interactive tasks. We update
 		 * an 'average sleep time' value here, based on
-		 * sleep_timestamp. The more time a task spends sleeping,
+		 * ->last_run. The more time a task spends sleeping,
 		 * the higher the average gets - and the higher the priority
 		 * boost gets as well.
 		 */
@@ -341,8 +347,7 @@ static inline void activate_task(task_t 
 			p->sleep_avg = MAX_SLEEP_AVG;
 		p->prio = effective_prio(p);
 	}
-	enqueue_task(p, array);
-	nr_running_inc(rq);
+	__activate_task(p, rq);
 }
 
 /*
@@ -460,6 +465,7 @@ static int try_to_wake_up(task_t * p, un
 	long old_state;
 	runqueue_t *rq;
 
+	sync &= SYNC_WAKEUPS;
 repeat_lock_task:
 	rq = task_rq_lock(p, &flags);
 	old_state = p->state;
@@ -479,12 +485,17 @@ repeat_lock_task:
 			}
 			if (old_state == TASK_UNINTERRUPTIBLE)
 				rq->nr_uninterruptible--;
-			activate_task(p, rq);
-	
-			if (p->prio < rq->curr->prio)
-				resched_task(rq->curr);
+			if (sync)
+				__activate_task(p, rq);
+			else {
+				activate_task(p, rq);
+				if (p->prio < rq->curr->prio)
+					resched_task(rq->curr);
+			}
 			success = 1;
 		}
+		if (p->state >= TASK_ZOMBIE)
+			BUG();
 		p->state = TASK_RUNNING;
 	}
 	task_rq_unlock(rq, &flags);
@@ -525,8 +536,19 @@ void wake_up_forked_process(task_t * p)
 		p->prio = effective_prio(p);
 	}
 	set_task_cpu(p, smp_processor_id());
-	activate_task(p, rq);
 
+	if (SMART_WAKE_CHILD) {
+		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++;
+		}
+	} else
+		activate_task(p, rq);
 	task_rq_unlock(rq, &flags);
 }
 
@@ -953,6 +975,11 @@ static inline void pull_task(runqueue_t 
 	 */
 	if (p->prio < this_rq->curr->prio)
 		set_need_resched();
+	else {
+		if (p->prio == this_rq->curr->prio &&
+				p->time_slice > this_rq->curr->time_slice)
+			set_need_resched();
+	}
 }
 
 /*
@@ -1016,7 +1043,7 @@ skip_queue:
 	 */
 
 #define CAN_MIGRATE_TASK(p,rq,this_cpu)					\
-	((jiffies - (p)->sleep_timestamp > cache_decay_ticks) &&	\
+	((jiffies - (p)->last_run > cache_decay_ticks) &&	\
 		!task_running(rq, p) &&					\
 			((p)->cpus_allowed & (1UL << (this_cpu))))
 
@@ -1076,9 +1103,9 @@ DEFINE_PER_CPU(struct kernel_stat, kstat
  * increasing number of running tasks:
  */
 #define EXPIRED_STARVING(rq) \
-		((rq)->expired_timestamp && \
+		(STARVATION_LIMIT && ((rq)->expired_timestamp && \
 		(jiffies - (rq)->expired_timestamp >= \
-			STARVATION_LIMIT * ((rq)->nr_running) + 1))
+			STARVATION_LIMIT * ((rq)->nr_running) + 1)))
 
 /*
  * This function gets called by the timer code, with HZ frequency.
@@ -1201,7 +1228,7 @@ need_resched:
 	rq = this_rq();
 
 	release_kernel_lock(prev);
-	prev->sleep_timestamp = jiffies;
+	prev->last_run = jiffies;
 	spin_lock_irq(&rq->lock);
 
 	/*
@@ -1701,7 +1728,7 @@ static int setscheduler(pid_t pid, int p
 	else
 		p->prio = p->static_prio;
 	if (array)
-		activate_task(p, task_rq(p));
+		__activate_task(p, task_rq(p));
 
 out_unlock:
 	task_rq_unlock(rq, &flags);
--- linux/kernel/fork.c.orig	
+++ linux/kernel/fork.c	
@@ -916,7 +916,7 @@ static struct task_struct *copy_process(
 	 */
 	p->first_time_slice = 1;
 	current->time_slice >>= 1;
-	p->sleep_timestamp = jiffies;
+	p->last_run = jiffies;
 	if (!current->time_slice) {
 		/*
 	 	 * This case is rare, it happens when the parent has only