From: Peter Zijlstra <a.p.zijlstra@chello.nl>
Date: Thu, 31 Jan 2008 21:45:22 +0000 (+0100)
Subject: sched: let +nice tasks have smaller impact
X-Git-Tag: v2.6.25-rc1~1126^2~2
X-Git-Url: https://err.no/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=ef9884e6f29bbe1075204f962a00f7533bf7e8f3;p=linux-2.6

sched: let +nice tasks have smaller impact

Michel Dänzr has bisected an interactivity problem with
plus-reniced tasks back to this commit:

 810e95ccd58d91369191aa4ecc9e6d4a10d8d0c8 is first bad commit
 commit 810e95ccd58d91369191aa4ecc9e6d4a10d8d0c8
 Author: Peter Zijlstra <a.p.zijlstra@chello.nl>
 Date:   Mon Oct 15 17:00:14 2007 +0200

 sched: another wakeup_granularity fix

      unit mis-match: wakeup_gran was used against a vruntime

fix this by assymetrically scaling the vtime of positive reniced
tasks.

Bisected-by: Michel Dänzer <michel@tungstengraphics.com>
Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
---

diff --git a/kernel/sched_fair.c b/kernel/sched_fair.c
index cf958aefac..6c091d6e15 100644
--- a/kernel/sched_fair.c
+++ b/kernel/sched_fair.c
@@ -1106,7 +1106,11 @@ static void check_preempt_wakeup(struct rq *rq, struct task_struct *p)
 	}
 
 	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)