Re: [PATCH] Staircase scheduler v7.4

[Con Kolivas <kernel@kolivas.org>]

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Con Kolivas wrote:
> 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.


Eeek that one I posted _was_ the one for ck kernels. This is the one for 
vanilla kernels with staircase7.4. Crikey I'm having a blowout here.

Con

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Index: linux-2.6.7-staircase/kernel/sched.c
===================================================================
--- linux-2.6.7-staircase.orig/kernel/sched.c	2004-06-25 02:24:34.000000000 +1000
+++ linux-2.6.7-staircase/kernel/sched.c	2004-06-27 21:49:48.912434799 +1000
@@ -218,8 +218,8 @@
 
 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);
@@ -255,7 +255,10 @@
 	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;
@@ -282,7 +285,10 @@
 		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;
@@ -291,7 +297,9 @@
 	return slice;
 }
 
-// interactive - interactive tasks get longer intervals at best priority
+/*
+ * interactive - sysctl which allows interactive tasks to have bursts
+ */
 int interactive = 1;
 
 /*
@@ -326,20 +334,25 @@
 	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->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->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);
@@ -764,7 +777,9 @@
 	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);
 
@@ -1746,11 +1761,15 @@
 	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);
@@ -3564,7 +3583,9 @@
 		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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