Re: [PATCH] Staircase scheduler v7.4

[Con Kolivas <kernel@kolivas.org>]

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Here is an incremental patch from 2.6.7-staircase7.4 (without any later 
changes) to staircase7.6 which I hope addresses your problem of no 
timeslice tasks. Can you try it please? Sorry about the previous noise.

Con

P.S.
Those with ck kernels I'm about to post another diff for -ck addressing 
the same thing.

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Index: linux-2.6.7-ck2pre/kernel/sched.c
===================================================================
--- linux-2.6.7-ck2pre.orig/kernel/sched.c	2004-06-25 23:06:57.000000000 +1000
+++ linux-2.6.7-ck2pre/kernel/sched.c	2004-06-27 21:39:40.182630568 +1000
@@ -231,8 +231,8 @@
 
 static void enqueue_task(struct task_struct *p, runqueue_t *rq)
 {
-	if (rq->curr->flags & PF_PREEMPTED) {
-		rq->curr->flags &= ~PF_PREEMPTED;
+	if (p->flags & PF_PREEMPTED) {
+		p->flags &= ~PF_PREEMPTED;
 		list_add(&p->run_list, rq->queue + p->prio);
 	} else
 		list_add_tail(&p->run_list, rq->queue + p->prio);
@@ -268,7 +268,10 @@
 	rq->nr_running++;
 }
 
-// burst - extra intervals an interactive task can run for at best priority
+/*
+ * burst - extra intervals an interactive task can run for at best priority
+ * instead of descending priorities.
+ */
 static unsigned int burst(task_t *p)
 {
 	unsigned int task_user_prio;
@@ -297,7 +300,10 @@
 		p->burst--;
 }
 
-// slice - the duration a task runs before losing burst
+/*
+ * slice - the duration a task runs before getting requeued at it's best
+ * priority and has it's burst decremented.
+ */
 static unsigned int slice(task_t *p)
 {
 	unsigned int slice = RR_INTERVAL;
@@ -308,7 +314,9 @@
 	return slice;
 }
 
-// interactive - interactive tasks get longer intervals at best priority
+/*
+ * interactive - sysctl which allows interactive tasks to have bursts
+ */
 int interactive = 1;
 
 /*
@@ -346,20 +354,25 @@
 	return prio;
 }
 
+/*
+ * recalc_task_prio - this checks for tasks that run ultra short timeslices
+ * or have just forked a thread/process and make them continue their old
+ * slice instead of starting a new one at high priority.
+ */
 static void recalc_task_prio(task_t *p, unsigned long long now)
 {
 	unsigned long sleep_time = now - p->timestamp;
-	unsigned long run_time = NS_TO_JIFFIES(p->runtime);
-	unsigned long total_run = NS_TO_JIFFIES(p->totalrun) + run_time;
-	if ((!run_time && NS_TO_JIFFIES(p->runtime + sleep_time) < 
-		rr_interval(p)) || p->flags & PF_FORKED) {
+	unsigned long ns_totalrun = p->totalrun + p->runtime;
+	unsigned long total_run = NS_TO_JIFFIES(ns_totalrun);
+	if (p->flags & PF_FORKED || (!(NS_TO_JIFFIES(p->runtime)) && 
+		NS_TO_JIFFIES(p->runtime + sleep_time) < rr_interval(p))) {
 			p->flags &= ~PF_FORKED;
 			if (p->slice - total_run < 1) {
 				p->totalrun = 0;
 				dec_burst(p);
 			} else {
-				p->totalrun += p->runtime;
-				p->slice -= NS_TO_JIFFIES(p->totalrun);
+				p->totalrun = ns_totalrun;
+				p->slice -= total_run;
 			}
 	} else {
 		inc_burst(p);
@@ -786,7 +799,9 @@
 	unsigned long flags;
 	runqueue_t *rq = task_rq_lock(current, &flags);
 
-	//Forked process gets no burst to prevent fork bombs.
+	/* 
+	 * Forked process gets no burst to prevent fork bombs.
+	 */
 	p->burst = 0;
 	BUG_ON(p->state != TASK_RUNNING);
 
@@ -1768,11 +1783,15 @@
 	cpustat->system += sys_ticks;
 
 	spin_lock(&rq->lock);
-	// SCHED_FIFO tasks never run out of timeslice.
+	/*
+	 * SCHED_FIFO tasks never run out of timeslice.
+	 */
 	if (unlikely(p->policy == SCHED_FIFO))
 		goto out_unlock;
 	rq->cache_ticks++;
-	// Tasks lose burst each time they use up a full slice().
+	/*
+	 * Tasks lose burst each time they use up a full slice().
+	 */
 	if (!--p->slice) {
 		set_tsk_need_resched(p);
 		dequeue_task(p, rq);
@@ -3601,7 +3620,9 @@
 		for (j = 0; j <= MAX_PRIO; j++)
 			INIT_LIST_HEAD(&rq->queue[j]);
 		memset(rq->bitmap, 0, BITS_TO_LONGS(MAX_PRIO+1)*sizeof(long));
-		// delimiter for bitsearch
+		/*
+		 * delimiter for bitsearch
+		 */
 		__set_bit(MAX_PRIO, rq->bitmap);
 	}
 	/*

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