On Tue, Sep 25, 2007 at 12:10:44PM +0200, Ingo Molnar wrote:
quoted text
> So the patch below just removes the is_same_group() condition. But i can 
> still see bad (and obvious) latencies with Mike's 2-hogs test:
> 
>  taskset 01 perl -e 'while (1) {}' &
>  nice -19 taskset 02 perl -e 'while (1) {}' &
> 
> So something's amiss.

While I try recreating this myself, I wonder if this patch helps?

---
 kernel/sched_fair.c |   19 ++++++++++++++-----
 1 file changed, 14 insertions(+), 5 deletions(-)

Index: current/kernel/sched_fair.c
===================================================================
--- current.orig/kernel/sched_fair.c
+++ current/kernel/sched_fair.c
@@ -794,7 +794,8 @@ static void yield_task_fair(struct rq *r
 static void check_preempt_wakeup(struct rq *rq, struct task_struct *p)
 {
 	struct task_struct *curr = rq->curr;
-	struct cfs_rq *cfs_rq = task_cfs_rq(curr);
+	struct cfs_rq *cfs_rq = task_cfs_rq(curr), *pcfs_rq;
+	struct sched_entity *se = &curr->se, *pse = &p->se;
 
 	if (unlikely(rt_prio(p->prio))) {
 		update_rq_clock(rq);
@@ -802,11 +803,19 @@ static void check_preempt_wakeup(struct 
 		resched_task(curr);
 		return;
 	}
-	if (is_same_group(curr, p)) {
-		s64 delta = curr->se.vruntime - p->se.vruntime;
 
-		if (delta > (s64)sysctl_sched_wakeup_granularity)
-			resched_task(curr);
+	for_each_sched_entity(se) {
+		cfs_rq = cfs_rq_of(se);
+		pcfs_rq = cfs_rq_of(pse);
+
+		if (cfs_rq == pcfs_rq) {
+			s64 delta = se->vruntime - pse->vruntime;
+
+			if (delta > (s64)sysctl_sched_wakeup_granularity)
+				resched_task(curr);
+			break;
+		}
+		pse = pse->parent;
 	}
 }
 

-- 
Regards,
vatsa
-
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