linux-kernel - Re: Regression in latest sched-git

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Date:	Thu, 14 Feb 2008 12:20:41 +0100
From:	Peter Zijlstra <a.p.zijlstra@...llo.nl>
To:	Dhaval Giani <dhaval@...ux.vnet.ibm.com>
Cc:	Ingo Molnar <mingo@...e.hu>,
	Srivatsa Vaddagiri <vatsa@...ux.vnet.ibm.com>,
	lkml <linux-kernel@...r.kernel.org>,
	Mike Galbraith <efault@....de>
Subject: Re: Regression in latest sched-git

Hi Dhaval,

How does this patch (on top of todays sched-devel.git) work for you?

It keeps my laptop nice and spiffy when I run

let i=0; while [ $i -lt 100 ]; do let i+=1; while :; do :; done & done

under a third user (nobody). This generates huge latencies for the nobody 
user (up to 1.6s) but root and peter don't seem to get above 40ms

---
 include/linux/sched.h |    1 +
 kernel/sched_fair.c   |    6 +++++-
 2 files changed, 6 insertions(+), 1 deletion(-)

Index: linux-2.6/include/linux/sched.h
===================================================================
--- linux-2.6.orig/include/linux/sched.h
+++ linux-2.6/include/linux/sched.h
@@ -925,6 +925,7 @@ struct sched_entity {
 	u64			exec_start;
 	u64			sum_exec_runtime;
 	u64			vruntime;
+	u64			vperiod;
 	u64			prev_sum_exec_runtime;
 
 #ifdef CONFIG_SCHEDSTATS
Index: linux-2.6/kernel/sched_fair.c
===================================================================
--- linux-2.6.orig/kernel/sched_fair.c
+++ linux-2.6/kernel/sched_fair.c
@@ -220,9 +220,11 @@ static inline u64 min_vruntime(u64 min_v
 
 static inline s64 entity_key(struct cfs_rq *cfs_rq, struct sched_entity *se)
 {
-	return se->vruntime - cfs_rq->min_vruntime;
+	return se->vruntime + se->vperiod - cfs_rq->min_vruntime;
 }
 
+static u64 sched_vslice_add(struct cfs_rq *cfs_rq, struct sched_entity *se);
+
 /*
  * Enqueue an entity into the rb-tree:
  */
@@ -240,6 +242,8 @@ static void __enqueue_entity(struct cfs_
 	if (se == cfs_rq->curr)
 		return;
 
+	se->vperiod = sched_vslice_add(cfs_rq, se);
+
 	cfs_rq = &rq_of(cfs_rq)->cfs;
 
 	link = &cfs_rq->tasks_timeline.rb_node;


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