sched: let +nice tasks have smaller impact

patch ef9884e6f29bbe1075204f962a00f7533bf7e8f3 in mainline.

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>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

diff --git a/kernel/sched_fair.c b/kernel/sched_fair.c
index da7c061e72062eacd6afee8a9870e9044ad0e2c5..94e88beb15f30f3bfafd69aaf9e6439a09a7746f 100644 (file)
--- a/kernel/sched_fair.c
+++ b/kernel/sched_fair.c
@@ -867,7 +867,11 @@ 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)