linux-kernel - Re: [Announce] [patch] Modular Scheduler Core and Completely Fair Scheduler [CFS]

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Date:	Sun, 15 Apr 2007 21:37:47 +0200
From:	Ingo Molnar <mingo@...e.hu>
To:	Willy Tarreau <w@....eu>
Cc:	"Eric W. Biederman" <ebiederm@...ssion.com>,
	Nick Piggin <npiggin@...e.de>, linux-kernel@...r.kernel.org,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Con Kolivas <kernel@...ivas.org>,
	Mike Galbraith <efault@....de>,
	Arjan van de Ven <arjan@...radead.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Jiri Slaby <jirislaby@...il.com>,
	Alan Cox <alan@...rguk.ukuu.org.uk>
Subject: Re: [Announce] [patch] Modular Scheduler Core and Completely Fair Scheduler [CFS]


* Ingo Molnar <mingo@...e.hu> wrote:

> so Linus was right: this was caused by scheduler starvation. I can see 
> one immediate problem already: the 'nice offset' is not divided by 
> nr_running as it should. The patch below should fix this but i have 
> yet to test it accurately, this change might as well render nice 
> levels unacceptably ineffective under high loads.

erm, rather the updated patch below if you want to use this on a 32-bit 
system. But ... i think you should wait until i have all this re-tested.

	Ingo

---
 include/linux/sched.h |    2 +-
 kernel/sched_fair.c   |    4 +++-
 2 files changed, 4 insertions(+), 2 deletions(-)

Index: linux/include/linux/sched.h
===================================================================
--- linux.orig/include/linux/sched.h
+++ linux/include/linux/sched.h
@@ -839,7 +839,7 @@ struct task_struct {
 
 	s64 wait_runtime;
 	u64 exec_runtime, fair_key;
-	s64 nice_offset, hog_limit;
+	s32 nice_offset, hog_limit;
 
 	unsigned long policy;
 	cpumask_t cpus_allowed;
Index: linux/kernel/sched_fair.c
===================================================================
--- linux.orig/kernel/sched_fair.c
+++ linux/kernel/sched_fair.c
@@ -31,7 +31,9 @@ static void __enqueue_task_fair(struct r
 	int leftmost = 1;
 	long long key;
 
-	key = rq->fair_clock - p->wait_runtime + p->nice_offset;
+	key = rq->fair_clock - p->wait_runtime;
+	if (unlikely(p->nice_offset))
+		key += p->nice_offset / (rq->nr_running + 1);
 
 	p->fair_key = key;
 
-
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