linux-kernel - Re: 2.6.24-git4+ regression

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Date:	Thu, 31 Jan 2008 11:29:19 +0100
From:	Ingo Molnar <mingo@...e.hu>
To:	Lukas Hejtmanek <xhejtman@....muni.cz>
Cc:	mingo@...hat.com, linux-kernel@...r.kernel.org,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>
Subject: Re: 2.6.24-git4+ regression


* Lukas Hejtmanek <xhejtman@....muni.cz> wrote:

> I noticed short thread in LKM regarding "sched: add vslice" causes 
> horrible interactivity under load.
> 
> I can see similar behavior. If I stress both CPU cores, even typing on 
> keyboard suffers from huge latencies, I can see letters appearing with 
> delay (typing into xterm). No swap is used at all, having 1GB free 
> RAM.
> 
> I noticed this bad behavior with 2.6.24-git[46], 2.6.24-rc8-git was 
> OK.

if you apply the current sched-fixes (rollup patch below), does it get 
any better?

	Ingo

Index: linux/kernel/sched_fair.c
===================================================================
--- linux.orig/kernel/sched_fair.c
+++ linux/kernel/sched_fair.c
@@ -520,7 +520,7 @@ place_entity(struct cfs_rq *cfs_rq, stru
 
 	if (!initial) {
 		/* sleeps upto a single latency don't count. */
-		if (sched_feat(NEW_FAIR_SLEEPERS) && entity_is_task(se))
+		if (sched_feat(NEW_FAIR_SLEEPERS))
 			vruntime -= sysctl_sched_latency;
 
 		/* ensure we never gain time by being placed backwards. */
@@ -1106,7 +1106,11 @@ static void check_preempt_wakeup(struct 
 	}
 
 	gran = sysctl_sched_wakeup_granularity;
-	if (unlikely(se->load.weight != NICE_0_LOAD))
+	/*
+	 * More easily preempt - nice tasks, while not making
+	 * it harder for + nice tasks.
+	 */
+	if (unlikely(se->load.weight > NICE_0_LOAD))
 		gran = calc_delta_fair(gran, &se->load);
 
 	if (pse->vruntime + gran < se->vruntime)
--
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