linux-kernel - Re: VolanoMark regression with 2.6.27-rc1

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Date:	Wed, 20 Aug 2008 15:32:17 +0200
From:	Peter Zijlstra <a.p.zijlstra@...llo.nl>
To:	Ingo Molnar <mingo@...e.hu>
Cc:	"Zhang, Yanmin" <yanmin_zhang@...ux.intel.com>,
	Dhaval Giani <dhaval@...ux.vnet.ibm.com>,
	LKML <linux-kernel@...r.kernel.org>,
	Srivatsa Vaddagiri <vatsa@...ux.vnet.ibm.com>,
	Aneesh Kumar KV <aneesh.kumar@...ux.vnet.ibm.com>,
	Balbir Singh <balbir@...ibm.com>,
	Chris Friesen <cfriesen@...tel.com>
Subject: Re: VolanoMark regression with 2.6.27-rc1

On Wed, 2008-08-20 at 12:51 +0200, Ingo Molnar wrote:
> * Peter Zijlstra <a.p.zijlstra@...llo.nl> wrote:
> 
> > And I must admit to having overlooked the effect on wake_affine..
> > 
> > Chris, could you see the effect of this on smp group fairness?

Just realized my brainfart..

---
Subject: sched: load-balance bias fixes
From: Peter Zijlstra <a.p.zijlstra@...llo.nl>
Date: Wed Aug 20 15:28:51 CEST 2008

Yanmin spotted a regression with my patch that introduces LB_BIAS:

  commit 93b75217df39e6d75889cc6f8050343286aff4a5
  Author: Peter Zijlstra <a.p.zijlstra@...llo.nl>
  Date:   Fri Jun 27 13:41:33 2008 +0200

And I just spotted the brainfart - I should have replaced min/max with avg
instead of removing it completely.

Signed-off-by: Peter Zijlstra <a.p.zijlstra@...llo.nl>
---
 include/linux/kernel.h |    6 ++++++
 kernel/sched.c         |   10 ++++++++--
 2 files changed, 14 insertions(+), 2 deletions(-)

Index: linux-2.6/include/linux/kernel.h
===================================================================
--- linux-2.6.orig/include/linux/kernel.h
+++ linux-2.6/include/linux/kernel.h
@@ -367,6 +367,12 @@ static inline char *pack_hex_byte(char *
 	(void) (&_max1 == &_max2);		\
 	_max1 > _max2 ? _max1 : _max2; })
 
+#define avg(x, y) ({				\
+	typeof(x) _avg1 = ((x)+1)/2;		\
+	typeof(x) _avg2 = ((y)+1)/2;		\
+	(void) (&_avg1 == &_avg2);		\
+	_avg1 + _avg2; })
+
 /**
  * clamp - return a value clamped to a given range with strict typechecking
  * @val: current value
Index: linux-2.6/kernel/sched.c
===================================================================
--- linux-2.6.orig/kernel/sched.c
+++ linux-2.6/kernel/sched.c
@@ -2008,9 +2008,12 @@ static unsigned long source_load(int cpu
 	struct rq *rq = cpu_rq(cpu);
 	unsigned long total = weighted_cpuload(cpu);
 
-	if (type == 0 || !sched_feat(LB_BIAS))
+	if (type == 0)
 		return total;
 
+	if (!sched_feat(LB_BIAS))
+		return avg(rq->cpu_load[type-1], total);
+
 	return min(rq->cpu_load[type-1], total);
 }
 
@@ -2023,9 +2026,12 @@ static unsigned long target_load(int cpu
 	struct rq *rq = cpu_rq(cpu);
 	unsigned long total = weighted_cpuload(cpu);
 
-	if (type == 0 || !sched_feat(LB_BIAS))
+	if (type == 0)
 		return total;
 
+	if (!sched_feat(LB_BIAS))
+		return avg(rq->cpu_load[type-1], total);
+
 	return max(rq->cpu_load[type-1], total);
 }
 


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