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Date: Fri, 17 Jan 2003 09:47:43 +0100 (CET)
From: Ingo Molnar <mingo@elte.hu>
Reply-To: Ingo Molnar <mingo@elte.hu>
To: "Martin J. Bligh" <mbligh@aracnet.com>
Cc: Christoph Hellwig <hch@infradead.org>, Robert Love <rml@tech9.net>,
       Erich Focht <efocht@ess.nec.de>, Michael Hohnbaum <hohnbaum@us.ibm.com>,
       Andrew Theurer <habanero@us.ibm.com>,
       Linus Torvalds <torvalds@transmeta.com>,
       linux-kernel <linux-kernel@vger.kernel.org>,
       lse-tech <lse-tech@lists.sourceforge.net>
Subject: [patch] sched-2.5.59-A2
In-Reply-To: <132930000.1042759915@flay>
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Martin, Erich,

could you give the attached patch a go, it implements my
cleanup/reorganization suggestions ontop of 2.5.59:

 - decouple the 'slow' rebalancer from the 'fast' rebalancer and attach it 
   to the scheduler tick. Remove rq->nr_balanced.

 - do idle-rebalancing every 1 msec, intra-node rebalancing every 200 
   msecs and inter-node rebalancing every 400 msecs.

 - move the tick-based rebalancing logic into rebalance_tick(), it looks
   more organized this way and we have all related code in one spot.

 - clean up the topology.h include file structure. Since generic kernel
   code uses all the defines already, there's no reason to keep them in
   asm-generic.h. I've created a linux/topology.h file that includes
   asm/topology.h and takes care of the default and generic definitions.
   Moved over a generic topology definition from mmzone.h.

 - renamed rq->prev_nr_running[] to rq->prev_cpu_load[] - this further
   unifies the SMP and NUMA balancers and is more in line with the
   prev_node_load name.

If performance drops due to this patch then the benchmarking goal would be
to tune the following frequencies:

 #define IDLE_REBALANCE_TICK (HZ/1000 ?: 1)
 #define BUSY_REBALANCE_TICK (HZ/5 ?: 1)
 #define NODE_REBALANCE_TICK (BUSY_REBALANCE_TICK * 2)

In theory NODE_REBALANCE_TICK could be defined by the NUMA platform,
although in the past such per-platform scheduler tunings used to end
'orphaned' after some time. 400 msecs is pretty conservative at the
moment, it could be made more frequent if benchmark results support it.

the patch compiles and boots on UP and SMP, it compiles on x86-NUMA.

	Ingo

--- linux/drivers/base/cpu.c.orig	2003-01-17 10:02:19.000000000 +0100
+++ linux/drivers/base/cpu.c	2003-01-17 10:02:25.000000000 +0100
@@ -6,8 +6,7 @@
 #include <linux/module.h>
 #include <linux/init.h>
 #include <linux/cpu.h>
-
-#include <asm/topology.h>
+#include <linux/topology.h>
 
 
 static int cpu_add_device(struct device * dev)
--- linux/drivers/base/node.c.orig	2003-01-17 10:02:50.000000000 +0100
+++ linux/drivers/base/node.c	2003-01-17 10:03:03.000000000 +0100
@@ -7,8 +7,7 @@
 #include <linux/init.h>
 #include <linux/mm.h>
 #include <linux/node.h>
-
-#include <asm/topology.h>
+#include <linux/topology.h>
 
 
 static int node_add_device(struct device * dev)
--- linux/drivers/base/memblk.c.orig	2003-01-17 10:02:33.000000000 +0100
+++ linux/drivers/base/memblk.c	2003-01-17 10:02:38.000000000 +0100
@@ -7,8 +7,7 @@
 #include <linux/init.h>
 #include <linux/memblk.h>
 #include <linux/node.h>
-
-#include <asm/topology.h>
+#include <linux/topology.h>
 
 
 static int memblk_add_device(struct device * dev)
--- linux/include/asm-generic/topology.h.orig	2003-01-17 09:49:38.000000000 +0100
+++ linux/include/asm-generic/topology.h	2003-01-17 10:02:08.000000000 +0100
@@ -1,56 +0,0 @@
-/*
- * linux/include/asm-generic/topology.h
- *
- * Written by: Matthew Dobson, IBM Corporation
- *
- * Copyright (C) 2002, IBM Corp.
- *
- * All rights reserved.          
- *
- * This program is free software; you can redistribute it and/or modify
- * it under the terms of the GNU General Public License as published by
- * the Free Software Foundation; either version 2 of the License, or
- * (at your option) any later version.
- *
- * This program is distributed in the hope that it will be useful, but
- * WITHOUT ANY WARRANTY; without even the implied warranty of
- * MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE, GOOD TITLE or
- * NON INFRINGEMENT.  See the GNU General Public License for more
- * details.
- *
- * You should have received a copy of the GNU General Public License
- * along with this program; if not, write to the Free Software
- * Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
- *
- * Send feedback to <colpatch@us.ibm.com>
- */
-#ifndef _ASM_GENERIC_TOPOLOGY_H
-#define _ASM_GENERIC_TOPOLOGY_H
-
-/* Other architectures wishing to use this simple topology API should fill
-   in the below functions as appropriate in their own <asm/topology.h> file. */
-#ifndef __cpu_to_node
-#define __cpu_to_node(cpu)		(0)
-#endif
-#ifndef __memblk_to_node
-#define __memblk_to_node(memblk)	(0)
-#endif
-#ifndef __parent_node
-#define __parent_node(node)		(0)
-#endif
-#ifndef __node_to_first_cpu
-#define __node_to_first_cpu(node)	(0)
-#endif
-#ifndef __node_to_cpu_mask
-#define __node_to_cpu_mask(node)	(cpu_online_map)
-#endif
-#ifndef __node_to_memblk
-#define __node_to_memblk(node)		(0)
-#endif
-
-/* Cross-node load balancing interval. */
-#ifndef NODE_BALANCE_RATE
-#define NODE_BALANCE_RATE 10
-#endif
-
-#endif /* _ASM_GENERIC_TOPOLOGY_H */
--- linux/include/asm-ppc64/topology.h.orig	2003-01-17 09:54:46.000000000 +0100
+++ linux/include/asm-ppc64/topology.h	2003-01-17 09:55:18.000000000 +0100
@@ -46,18 +46,6 @@
 	return mask;
 }
 
-/* Cross-node load balancing interval. */
-#define NODE_BALANCE_RATE 10
-
-#else /* !CONFIG_NUMA */
-
-#define __cpu_to_node(cpu)		(0)
-#define __memblk_to_node(memblk)	(0)
-#define __parent_node(nid)		(0)
-#define __node_to_first_cpu(node)	(0)
-#define __node_to_cpu_mask(node)	(cpu_online_map)
-#define __node_to_memblk(node)		(0)
-
 #endif /* CONFIG_NUMA */
 
 #endif /* _ASM_PPC64_TOPOLOGY_H */
--- linux/include/linux/topology.h.orig	2003-01-17 09:57:20.000000000 +0100
+++ linux/include/linux/topology.h	2003-01-17 10:09:38.000000000 +0100
@@ -0,0 +1,43 @@
+/*
+ * linux/include/linux/topology.h
+ */
+#ifndef _LINUX_TOPOLOGY_H
+#define _LINUX_TOPOLOGY_H
+
+#include <asm/topology.h>
+
+/*
+ * The default (non-NUMA) topology definitions:
+ */
+#ifndef __cpu_to_node
+#define __cpu_to_node(cpu)		(0)
+#endif
+#ifndef __memblk_to_node
+#define __memblk_to_node(memblk)	(0)
+#endif
+#ifndef __parent_node
+#define __parent_node(node)		(0)
+#endif
+#ifndef __node_to_first_cpu
+#define __node_to_first_cpu(node)	(0)
+#endif
+#ifndef __cpu_to_node_mask
+#define __cpu_to_node_mask(cpu)		(cpu_online_map)
+#endif
+#ifndef __node_to_cpu_mask
+#define __node_to_cpu_mask(node)		(cpu_online_map)
+#endif
+#ifndef __node_to_memblk
+#define __node_to_memblk(node)		(0)
+#endif
+
+#ifndef __cpu_to_node_mask
+#define __cpu_to_node_mask(cpu)		__node_to_cpu_mask(__cpu_to_node(cpu))
+#endif
+
+/*
+ * Generic defintions:
+ */
+#define numa_node_id()			(__cpu_to_node(smp_processor_id()))
+
+#endif /* _LINUX_TOPOLOGY_H */
--- linux/include/linux/mmzone.h.orig	2003-01-17 09:58:20.000000000 +0100
+++ linux/include/linux/mmzone.h	2003-01-17 10:01:17.000000000 +0100
@@ -255,9 +255,7 @@
 #define MAX_NR_MEMBLKS	1
 #endif /* CONFIG_NUMA */
 
-#include <asm/topology.h>
-/* Returns the number of the current Node. */
-#define numa_node_id()		(__cpu_to_node(smp_processor_id()))
+#include <linux/topology.h>
 
 #ifndef CONFIG_DISCONTIGMEM
 extern struct pglist_data contig_page_data;
--- linux/include/asm-ia64/topology.h.orig	2003-01-17 09:54:33.000000000 +0100
+++ linux/include/asm-ia64/topology.h	2003-01-17 09:54:38.000000000 +0100
@@ -60,7 +60,4 @@
  */
 #define __node_to_memblk(node) (node)
 
-/* Cross-node load balancing interval. */
-#define NODE_BALANCE_RATE 10
-
 #endif /* _ASM_IA64_TOPOLOGY_H */
--- linux/include/asm-i386/topology.h.orig	2003-01-17 09:55:28.000000000 +0100
+++ linux/include/asm-i386/topology.h	2003-01-17 09:56:27.000000000 +0100
@@ -61,17 +61,6 @@
 /* Returns the number of the first MemBlk on Node 'node' */
 #define __node_to_memblk(node) (node)
 
-/* Cross-node load balancing interval. */
-#define NODE_BALANCE_RATE 100
-
-#else /* !CONFIG_NUMA */
-/*
- * Other i386 platforms should define their own version of the 
- * above macros here.
- */
-
-#include <asm-generic/topology.h>
-
 #endif /* CONFIG_NUMA */
 
 #endif /* _ASM_I386_TOPOLOGY_H */
--- linux/include/asm-i386/cpu.h.orig	2003-01-17 10:03:22.000000000 +0100
+++ linux/include/asm-i386/cpu.h	2003-01-17 10:03:31.000000000 +0100
@@ -3,8 +3,8 @@
 
 #include <linux/device.h>
 #include <linux/cpu.h>
+#include <linux/topology.h>
 
-#include <asm/topology.h>
 #include <asm/node.h>
 
 struct i386_cpu {
--- linux/include/asm-i386/node.h.orig	2003-01-17 10:04:02.000000000 +0100
+++ linux/include/asm-i386/node.h	2003-01-17 10:04:08.000000000 +0100
@@ -4,8 +4,7 @@
 #include <linux/device.h>
 #include <linux/mmzone.h>
 #include <linux/node.h>
-
-#include <asm/topology.h>
+#include <linux/topology.h>
 
 struct i386_node {
 	struct node node;
--- linux/include/asm-i386/memblk.h.orig	2003-01-17 10:03:51.000000000 +0100
+++ linux/include/asm-i386/memblk.h	2003-01-17 10:03:56.000000000 +0100
@@ -4,8 +4,8 @@
 #include <linux/device.h>
 #include <linux/mmzone.h>
 #include <linux/memblk.h>
+#include <linux/topology.h>
 
-#include <asm/topology.h>
 #include <asm/node.h>
 
 struct i386_memblk {
--- linux/kernel/sched.c.orig	2003-01-17 09:22:24.000000000 +0100
+++ linux/kernel/sched.c	2003-01-17 10:29:53.000000000 +0100
@@ -153,10 +153,9 @@
 			nr_uninterruptible;
 	task_t *curr, *idle;
 	prio_array_t *active, *expired, arrays[2];
-	int prev_nr_running[NR_CPUS];
+	int prev_cpu_load[NR_CPUS];
 #ifdef CONFIG_NUMA
 	atomic_t *node_nr_running;
-	unsigned int nr_balanced;
 	int prev_node_load[MAX_NUMNODES];
 #endif
 	task_t *migration_thread;
@@ -765,29 +764,6 @@
 	return node;
 }
 
-static inline unsigned long cpus_to_balance(int this_cpu, runqueue_t *this_rq)
-{
-	int this_node = __cpu_to_node(this_cpu);
-	/*
-	 * Avoid rebalancing between nodes too often.
-	 * We rebalance globally once every NODE_BALANCE_RATE load balances.
-	 */
-	if (++(this_rq->nr_balanced) == NODE_BALANCE_RATE) {
-		int node = find_busiest_node(this_node);
-		this_rq->nr_balanced = 0;
-		if (node >= 0)
-			return (__node_to_cpu_mask(node) | (1UL << this_cpu));
-	}
-	return __node_to_cpu_mask(this_node);
-}
-
-#else /* !CONFIG_NUMA */
-
-static inline unsigned long cpus_to_balance(int this_cpu, runqueue_t *this_rq)
-{
-	return cpu_online_map;
-}
-
 #endif /* CONFIG_NUMA */
 
 #if CONFIG_SMP
@@ -807,10 +783,10 @@
 			spin_lock(&busiest->lock);
 			spin_lock(&this_rq->lock);
 			/* Need to recalculate nr_running */
-			if (idle || (this_rq->nr_running > this_rq->prev_nr_running[this_cpu]))
+			if (idle || (this_rq->nr_running > this_rq->prev_cpu_load[this_cpu]))
 				nr_running = this_rq->nr_running;
 			else
-				nr_running = this_rq->prev_nr_running[this_cpu];
+				nr_running = this_rq->prev_cpu_load[this_cpu];
 		} else
 			spin_lock(&busiest->lock);
 	}
@@ -847,10 +823,10 @@
 	 * that case we are less picky about moving a task across CPUs and
 	 * take what can be taken.
 	 */
-	if (idle || (this_rq->nr_running > this_rq->prev_nr_running[this_cpu]))
+	if (idle || (this_rq->nr_running > this_rq->prev_cpu_load[this_cpu]))
 		nr_running = this_rq->nr_running;
 	else
-		nr_running = this_rq->prev_nr_running[this_cpu];
+		nr_running = this_rq->prev_cpu_load[this_cpu];
 
 	busiest = NULL;
 	max_load = 1;
@@ -859,11 +835,11 @@
 			continue;
 
 		rq_src = cpu_rq(i);
-		if (idle || (rq_src->nr_running < this_rq->prev_nr_running[i]))
+		if (idle || (rq_src->nr_running < this_rq->prev_cpu_load[i]))
 			load = rq_src->nr_running;
 		else
-			load = this_rq->prev_nr_running[i];
-		this_rq->prev_nr_running[i] = rq_src->nr_running;
+			load = this_rq->prev_cpu_load[i];
+		this_rq->prev_cpu_load[i] = rq_src->nr_running;
 
 		if ((load > max_load) && (rq_src != this_rq)) {
 			busiest = rq_src;
@@ -922,7 +898,7 @@
  * We call this with the current runqueue locked,
  * irqs disabled.
  */
-static void load_balance(runqueue_t *this_rq, int idle)
+static void load_balance(runqueue_t *this_rq, int idle, unsigned long cpumask)
 {
 	int imbalance, idx, this_cpu = smp_processor_id();
 	runqueue_t *busiest;
@@ -930,8 +906,7 @@
 	struct list_head *head, *curr;
 	task_t *tmp;
 
-	busiest = find_busiest_queue(this_rq, this_cpu, idle, &imbalance,
-					cpus_to_balance(this_cpu, this_rq));
+	busiest = find_busiest_queue(this_rq, this_cpu, idle, &imbalance, cpumask);
 	if (!busiest)
 		goto out;
 
@@ -1006,21 +981,61 @@
  * frequency and balancing agressivity depends on whether the CPU is
  * idle or not.
  *
- * busy-rebalance every 250 msecs. idle-rebalance every 1 msec. (or on
+ * busy-rebalance every 200 msecs. idle-rebalance every 1 msec. (or on
  * systems with HZ=100, every 10 msecs.)
+ *
+ * On NUMA, do a node-rebalance every 400 msecs.
  */
-#define BUSY_REBALANCE_TICK (HZ/4 ?: 1)
 #define IDLE_REBALANCE_TICK (HZ/1000 ?: 1)
+#define BUSY_REBALANCE_TICK (HZ/5 ?: 1)
+#define NODE_REBALANCE_TICK (BUSY_REBALANCE_TICK * 2)
 
-static inline void idle_tick(runqueue_t *rq)
+static void rebalance_tick(runqueue_t *this_rq, int idle)
 {
-	if (jiffies % IDLE_REBALANCE_TICK)
+	int this_cpu = smp_processor_id();
+	unsigned long j = jiffies, cpumask, this_cpumask = 1UL << this_cpu;
+
+	if (idle) {
+		if (!(j % IDLE_REBALANCE_TICK)) {
+			spin_lock(&this_rq->lock);
+			load_balance(this_rq, 1, this_cpumask);
+			spin_unlock(&this_rq->lock);
+		}
 		return;
-	spin_lock(&rq->lock);
-	load_balance(rq, 1);
-	spin_unlock(&rq->lock);
+	}
+	/*
+	 * First do inter-node rebalancing, then intra-node rebalancing,
+	 * if both events happen in the same tick. The inter-node
+	 * rebalancing does not necessarily have to create a perfect
+	 * balance within the node, since we load-balance the most loaded
+	 * node with the current CPU. (ie. other CPUs in the local node
+	 * are not balanced.)
+	 */
+#if CONFIG_NUMA
+	if (!(j % NODE_REBALANCE_TICK)) {
+		int node = find_busiest_node(__cpu_to_node(this_cpu));
+		if (node >= 0) {
+			cpumask = __node_to_cpu_mask(node) | this_cpumask;
+			spin_lock(&this_rq->lock);
+			load_balance(this_rq, 1, cpumask);
+			spin_unlock(&this_rq->lock);
+		}
+	}
+#endif
+	if (!(j % BUSY_REBALANCE_TICK)) {
+		cpumask = __cpu_to_node_mask(this_cpu);
+		spin_lock(&this_rq->lock);
+		load_balance(this_rq, 1, cpumask);
+		spin_unlock(&this_rq->lock);
+	}
+}
+#else
+/*
+ * on UP we do not need to balance between CPUs:
+ */
+static inline void rebalance_tick(runqueue_t *this_rq, int idle)
+{
 }
-
 #endif
 
 DEFINE_PER_CPU(struct kernel_stat, kstat) = { { 0 } };
@@ -1063,9 +1078,7 @@
 			kstat_cpu(cpu).cpustat.iowait += sys_ticks;
 		else
 			kstat_cpu(cpu).cpustat.idle += sys_ticks;
-#if CONFIG_SMP
-		idle_tick(rq);
-#endif
+		rebalance_tick(rq, 1);
 		return;
 	}
 	if (TASK_NICE(p) > 0)
@@ -1121,11 +1134,8 @@
 			enqueue_task(p, rq->active);
 	}
 out:
-#if CONFIG_SMP
-	if (!(jiffies % BUSY_REBALANCE_TICK))
-		load_balance(rq, 0);
-#endif
 	spin_unlock(&rq->lock);
+	rebalance_tick(rq, 0);
 }
 
 void scheduling_functions_start_here(void) { }
@@ -1184,7 +1194,7 @@
 pick_next_task:
 	if (unlikely(!rq->nr_running)) {
 #if CONFIG_SMP
-		load_balance(rq, 1);
+		load_balance(rq, 1, __cpu_to_node_mask(smp_processor_id()));
 		if (rq->nr_running)
 			goto pick_next_task;
 #endif
--- linux/mm/page_alloc.c.orig	2003-01-17 10:01:29.000000000 +0100
+++ linux/mm/page_alloc.c	2003-01-17 10:01:35.000000000 +0100
@@ -28,8 +28,7 @@
 #include <linux/blkdev.h>
 #include <linux/slab.h>
 #include <linux/notifier.h>
-
-#include <asm/topology.h>
+#include <linux/topology.h>
 
 DECLARE_BITMAP(node_online_map, MAX_NUMNODES);
 DECLARE_BITMAP(memblk_online_map, MAX_NR_MEMBLKS);
--- linux/mm/vmscan.c.orig	2003-01-17 10:01:44.000000000 +0100
+++ linux/mm/vmscan.c	2003-01-17 10:01:52.000000000 +0100
@@ -27,10 +27,10 @@
 #include <linux/pagevec.h>
 #include <linux/backing-dev.h>
 #include <linux/rmap-locking.h>
+#include <linux/topology.h>
 
 #include <asm/pgalloc.h>
 #include <asm/tlbflush.h>
-#include <asm/topology.h>
 #include <asm/div64.h>
 
 #include <linux/swapops.h>

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