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From: Kai Bankett <kai.bankett@ontika.net>
Organization: ChaosNET IG
To: mingo@redhat.com, linux-kernel@vger.kernel.org
Subject: [PATCH][IO_APIC] 2.5.63bk7 irq_balance improvments / bug-fixes
Date: Tue, 4 Mar 2003 17:33:14 +0100
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Hi,

This patch does the following things :

* Bouncing of IRQs between CPUs reduction
  If IRQ already moved - check if further move makes sense
  (blocks bounce forth and back)

* Bring back interrupts to the IRQ_PRIMARY_CPU (default = 0)
  If interupts / time drops down the IRQ is routed back to the default CPU

* Introduces a desc_interrupt[irq].processor value
  This is needed to decide which IRQ has to be routed back to the default CPU.

* Add visualization for desc_interrupt[irq].processor value in
  '/proc/interrupt'

* If less than 2 CPUs online on boot-time kirqd is not started
  At least the rest of the logic wouldn't be able to recognize added CPUs at a
  later time.

* FIX timer_irq_works() - used a 'unsigned int' to store jiffies value

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 arch/i386/kernel/io_apic.c  |  118 +++++++++++++++++++++++++++++---------------
 arch/i386/kernel/irq.c      |   11 ++++
 arch/i386/kernel/irq.c.orig |only
 include/linux/irq.h         |    3 +
 4 files changed, 92 insertions(+), 40 deletions(-)

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diff -u -r linux-2.5.63/arch/i386/kernel/io_apic.c linux-2.5.63.new/arch/i386/kernel/io_apic.c
--- linux-2.5.63/arch/i386/kernel/io_apic.c	2003-03-04 13:07:12.000000000 +0100
+++ linux-2.5.63.new/arch/i386/kernel/io_apic.c	2003-03-04 13:43:40.000000000 +0100
@@ -18,6 +18,8 @@
  *					and Rolf G. Tews
  *					for testing these extensively
  *	Paul Diefenbaugh	:	Added full ACPI support
+ *	Kai Bankett		:	Improved interrupt distribution
+ *					and stickiness
  */
 
 #include <linux/mm.h>
@@ -214,7 +216,7 @@
 # include <linux/timer.h>	/* time_after() */
  
 # if CONFIG_BALANCED_IRQ_DEBUG
-#  define TDprintk(x...) do { printk("<%ld:%s:%d>: ", jiffies, __FILE__, __LINE__); printk(x); } while (0)
+#  define TDprintk(x...) do { printk("<%lu:%s:%d>: ", jiffies, __FILE__, __LINE__); printk(x); } while (0)
 #  define Dprintk(x...) do { TDprintk(x); } while (0)
 # else
 #  define TDprintk(x...) 
@@ -232,9 +234,17 @@
 	unsigned long irq;
 } irq_cpu_data[NR_CPUS];
 
+struct irq_cpu_sum {
+	unsigned long total;
+} irq_cpu_total[NR_CPUS];
+
+/* fall back to this CPU-no for all interrupts */
+#define IRQ_PRIMARY_CPU 0
+
 #define CPU_IRQ(cpu)		(irq_cpu_data[cpu].irq)
 #define LAST_CPU_IRQ(cpu,irq)   (irq_cpu_data[cpu].last_irq[irq])
 #define IRQ_DELTA(cpu,irq) 	(irq_cpu_data[cpu].irq_delta[irq])
+#define CPU_IRQ_TOTAL(cpu)	(irq_cpu_total[cpu].total)
 
 #define IDLE_ENOUGH(cpu,now) \
 		(idle_cpu(cpu) && ((now) - irq_stat[(cpu)].idle_timestamp > 1))
@@ -252,7 +262,7 @@
 
 long balanced_irq_interval = MAX_BALANCED_IRQ_INTERVAL;
 					 
-static inline void balance_irq(int cpu, int irq);
+static inline void balance_irq(int cpu, int irq, int on_primary);
 
 static inline void rotate_irqs_among_cpus(unsigned long useful_load_threshold)
 {
@@ -265,7 +275,8 @@
 			/* Is it a significant load ?  */
 			if (IRQ_DELTA(CPU_TO_PACKAGEINDEX(i),j) < useful_load_threshold)
 				continue;
-			balance_irq(i, j);
+			/* balance (no primary force) */
+			balance_irq(i, j, 0);
 		}
 	}
 	balanced_irq_interval = max((long)MIN_BALANCED_IRQ_INTERVAL,
@@ -279,7 +290,7 @@
 	unsigned long max_cpu_irq = 0, min_cpu_irq = (~0);
 	unsigned long move_this_load = 0;
 	int max_loaded = 0, min_loaded = 0;
-	unsigned long useful_load_threshold = balanced_irq_interval + 10;
+	unsigned long useful_load_threshold = balanced_irq_interval + 200;
 	int selected_irq;
 	int tmp_loaded, first_attempt = 1;
 	unsigned long tmp_cpu_irq;
@@ -293,6 +304,7 @@
 		if (!cpu_online(i))
 			continue;
 		package_index = CPU_TO_PACKAGEINDEX(i);
+		CPU_IRQ_TOTAL(package_index) = 0;
 		for (j = 0; j < NR_IRQS; j++) {
 			unsigned long value_now, delta;
 			/* Is this an active IRQ? */
@@ -306,6 +318,18 @@
 			/* Determine the activity per processor per IRQ */
 			delta = value_now - LAST_CPU_IRQ(i,j);
 
+			/* Switch back to primary cpu if not loaded */
+			if ((i == irq_desc[j].processor) &&
+			    (delta < useful_load_threshold) &&
+			    (irq_desc[j].processor != IRQ_PRIMARY_CPU)) {
+				/* move back irq */
+				balance_irq(irq_desc[j].processor,j,1);
+				continue;
+			}
+
+			/* update irq total counter */
+			CPU_IRQ_TOTAL(package_index) += delta;
+
 			/* Update last_cpu_irq[][] for the next time */
 			LAST_CPU_IRQ(i,j) = value_now;
 
@@ -441,6 +465,7 @@
 		Dprintk("irq = %d moved to cpu = %d\n", selected_irq, min_loaded);
 		/* mark for change destination */
 		spin_lock(&desc->lock);
+		irq_desc[selected_irq].processor = min_loaded;
 		pending_irq_balance_apicid[selected_irq] = cpu_to_logical_apicid(min_loaded);
 		spin_unlock(&desc->lock);
 		/* Since we made a change, come back sooner to 
@@ -460,62 +485,75 @@
 	return;
 }
 
-static unsigned long move(int curr_cpu, unsigned long allowed_mask, unsigned long now, int direction)
+static inline void balance_irq (int cpu, int irq, int on_primary)
 {
-	int search_idle = 1;
-	int cpu = curr_cpu;
-
-	goto inside;
-
-	do {
-		if (unlikely(cpu == curr_cpu))
-			search_idle = 0;
-inside:
-		if (direction == 1) {
-			cpu++;
-			if (cpu >= NR_CPUS)
-				cpu = 0;
-		} else {
-			cpu--;
-			if (cpu == -1)
-				cpu = NR_CPUS-1;
-		}
-	} while (!cpu_online(cpu) || !IRQ_ALLOWED(cpu,allowed_mask) ||
-			(search_idle && !IDLE_ENOUGH(cpu,now)));
-
-	return cpu;
-}
-
-static inline void balance_irq (int cpu, int irq)
-{
-	unsigned long now = jiffies;
 	unsigned long allowed_mask;
-	unsigned int new_cpu;
+	unsigned long tmp_cur_irq;
+	unsigned int i, new_cpu;
 		
 	if (irqbalance_disabled)
 		return;
 
 	allowed_mask = cpu_online_map & irq_affinity[irq];
-	new_cpu = move(cpu, allowed_mask, now, 1);
+
+	if (on_primary == 1) {
+		new_cpu = IRQ_PRIMARY_CPU;
+		goto do_work;
+	}
+
+	/* Does ist make sense to balance ? */
+	new_cpu = IRQ_PRIMARY_CPU;
+	tmp_cur_irq = ULONG_MAX;
+
+	for (i = 0; i < NR_CPUS; i++) {
+		if (!cpu_online(i) || !IRQ_ALLOWED(i,allowed_mask))
+			continue;
+		if (CPU_IRQ_TOTAL(CPU_TO_PACKAGEINDEX(i)) < tmp_cur_irq) {
+			tmp_cur_irq = CPU_IRQ_TOTAL(CPU_TO_PACKAGEINDEX(i));
+			new_cpu = i;
+		}
+	}
+	if (CPU_IRQ_TOTAL(CPU_TO_PACKAGEINDEX(new_cpu)) + IRQ_DELTA(CPU_TO_PACKAGEINDEX(cpu),irq)
+			>= CPU_IRQ_TOTAL(CPU_TO_PACKAGEINDEX(cpu))) {
+		Dprintk("balanced_irq: Balance makes no sense\n");
+		return;
+	}
+
+do_work:
 	if (cpu != new_cpu) {
 		irq_desc_t *desc = irq_desc + irq;
 		spin_lock(&desc->lock);
+		irq_desc[irq].processor = new_cpu;
 		pending_irq_balance_apicid[irq] = cpu_to_logical_apicid(new_cpu);
 		spin_unlock(&desc->lock);
-	}
+	} else
+		Dprintk("balance_irq: irq-switch senseless (cpu == new_cpu)\n");
 }
 
 int balanced_irq(void *unused)
 {
 	int i;
+	int cpu_count = 0;
 	unsigned long prev_balance_time = jiffies;
 	long time_remaining = balanced_irq_interval;
 
+	/* push everything to CPU(IRQ_PRIMRAY_CPU)
+	   to give us a starting point. */
+	for (i = 0; i < NR_IRQS; i++) {
+		pending_irq_balance_apicid[i] = cpu_to_logical_apicid(IRQ_PRIMARY_CPU);
+		irq_desc[i].processor = 0;
+	}
+
+	/* if running only with one cpu - balance_irq does not make sense */
+	for (i = 0; i < NR_CPUS; i++) {
+		if (cpu_online(i))
+			cpu_count++;
+	}
+	if (cpu_count < 2)
+		return 0;
+
 	daemonize("kirqd");
 	
-	/* push everything to CPU 0 to give us a starting point.  */
-	for (i = 0 ; i < NR_IRQS ; i++)
-		pending_irq_balance_apicid[i] = cpu_to_logical_apicid(0);
 	for (;;) {
 		set_current_state(TASK_INTERRUPTIBLE);
 		time_remaining = schedule_timeout(time_remaining);
@@ -1566,7 +1604,7 @@
  */
 static int __init timer_irq_works(void)
 {
-	unsigned int t1 = jiffies;
+	unsigned long t1 = jiffies;
 
 	local_irq_enable();
 	/* Let ten ticks pass... */
@@ -1579,7 +1617,7 @@
 	 * might have cached one ExtINT interrupt.  Finally, at
 	 * least one tick may be lost due to delays.
 	 */
-	if (jiffies - t1 > 4)
+	if (time_after(jiffies, t1 + 4))
 		return 1;
 
 	return 0;
diff -u -r linux-2.5.63/arch/i386/kernel/irq.c linux-2.5.63.new/arch/i386/kernel/irq.c
--- linux-2.5.63/arch/i386/kernel/irq.c	2003-03-04 13:07:12.000000000 +0100
+++ linux-2.5.63.new/arch/i386/kernel/irq.c	2003-03-04 13:18:22.000000000 +0100
@@ -65,8 +65,13 @@
 /*
  * Controller mappings for all interrupt sources:
  */
+#if defined(CONFIG_X86_IO_APIC)
+irq_desc_t irq_desc[NR_IRQS] __cacheline_aligned =
+	{ [0 ... NR_IRQS-1] = { 0, &no_irq_type, NULL, 0, 0, SPIN_LOCK_UNLOCKED}};
+#else
 irq_desc_t irq_desc[NR_IRQS] __cacheline_aligned =
 	{ [0 ... NR_IRQS-1] = { 0, &no_irq_type, NULL, 0, SPIN_LOCK_UNLOCKED}};
+#endif
 
 static void register_irq_proc (unsigned int irq);
 
@@ -140,6 +145,9 @@
 	for (j=0; j<NR_CPUS; j++)
 		if (cpu_online(j))
 			p += seq_printf(p, "CPU%d       ",j);
+#if CONFIG_X86_IO_APIC
+	p += seq_printf(p, "ON_CPU");
+#endif
 	seq_putc(p, '\n');
 
 	for (i = 0 ; i < NR_IRQS ; i++) {
@@ -155,6 +163,9 @@
 				p += seq_printf(p, "%10u ",
 					     kstat_cpu(j).irqs[i]);
 #endif
+#if CONFIG_X86_IO_APIC
+		seq_printf(p, " %11i", irq_desc[i].processor);
+#endif
 		seq_printf(p, " %14s", irq_desc[i].handler->typename);
 		seq_printf(p, "  %s", action->name);
 
Only in linux-2.5.63.new/arch/i386/kernel: irq.c.orig
diff -u -r linux-2.5.63/include/linux/irq.h linux-2.5.63.new/include/linux/irq.h
--- linux-2.5.63/include/linux/irq.h	2003-02-24 20:05:29.000000000 +0100
+++ linux-2.5.63.new/include/linux/irq.h	2003-03-03 12:37:06.000000000 +0100
@@ -61,6 +61,9 @@
 	hw_irq_controller *handler;
 	struct irqaction *action;	/* IRQ action list */
 	unsigned int depth;		/* nested irq disables */
+#if defined(CONFIG_X86_IO_APIC)
+	unsigned int processor;
+#endif
 	spinlock_t lock;
 } ____cacheline_aligned irq_desc_t;
 

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