[patch] config option for irq_balance()

[Matthew Dobson <colpatch@us.ibm.com>]

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IRQ Balancing doesn't work on some hardware platforms or systems with > 8 CPUs. 
  Some benchmarks have also showed that the irq_balancing code is actually a 
performance hit in many cases.  For these reasons, I've created a config option 
to turn of IRQ Balancing if desired.  Attatched is the patch...

Cheers!

-Matt


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diff -Nur linux-2.5.25-vanilla/arch/i386/Config.help linux-2.5.25-patched/arch/i386/Config.help
--- linux-2.5.25-vanilla/arch/i386/Config.help	Fri Jul  5 16:42:04 2002
+++ linux-2.5.25-patched/arch/i386/Config.help	Thu Jul 11 17:27:01 2002
@@ -41,6 +41,12 @@
   486, 586, Pentiums, and various instruction-set-compatible chips by
   AMD, Cyrix, and others.
 
+CONFIG_IRQ_BALANCE
+  This option is used to turn IRQ Balancing on machines with multiple
+  APIC's (ie: SMP, NUMA, etc) on or off.  This behavior has been seen 
+  under some conditions to reduce performance, and on some platorms causes
+  interesting hangs, particularly those with more than 8 CPUs.
+
 CONFIG_MULTIQUAD
   This option is used for getting Linux to run on a (IBM/Sequent) NUMA 
   multiquad box. This changes the way that processors are bootstrapped,
diff -Nur linux-2.5.25-vanilla/arch/i386/config.in linux-2.5.25-patched/arch/i386/config.in
--- linux-2.5.25-vanilla/arch/i386/config.in	Fri Jul  5 16:42:20 2002
+++ linux-2.5.25-patched/arch/i386/config.in	Thu Jul 11 17:16:52 2002
@@ -164,8 +164,19 @@
    if [ "$CONFIG_X86_UP_IOAPIC" = "y" ]; then
       define_bool CONFIG_X86_IO_APIC y
    fi
+   define_bool CONFIG_IRQBALANCE n
 else
    bool 'Multiquad NUMA system' CONFIG_MULTIQUAD
+   if [ "$CONFIG_MULTIQUAD" = "y" ]; then
+      define_bool CONFIG_IRQBALANCE_DISABLE y
+   else
+      bool 'Turn Off IRQ Balancing' CONFIG_IRQBALANCE_DISABLE
+   fi
+   if [ "$CONFIG_IRQBALANCE_DISABLE" = "y" ]; then
+      define_bool CONFIG_IRQBALANCE n
+   else
+      define_bool CONFIG_IRQBALANCE y
+   fi
 fi
 
 bool 'Machine Check Exception' CONFIG_X86_MCE
diff -Nur linux-2.5.25-vanilla/arch/i386/kernel/io_apic.c linux-2.5.25-patched/arch/i386/kernel/io_apic.c
--- linux-2.5.25-vanilla/arch/i386/kernel/io_apic.c	Fri Jul  5 16:42:20 2002
+++ linux-2.5.25-patched/arch/i386/kernel/io_apic.c	Thu Jul 11 16:12:28 2002
@@ -199,7 +199,7 @@
 	spin_unlock_irqrestore(&ioapic_lock, flags);
 }
 
-#if CONFIG_SMP
+#if CONFIG_IRQBALANCE
 
 typedef struct {
 	unsigned int cpu;
@@ -211,15 +211,12 @@
 
 extern unsigned long irq_affinity [NR_IRQS];
 
-#endif
-
 #define IDLE_ENOUGH(cpu,now) \
 		(idle_cpu(cpu) && ((now) - irq_stat[(cpu)].idle_timestamp > 1))
 
 #define IRQ_ALLOWED(cpu,allowed_mask) \
 		((1 << cpu) & (allowed_mask))
 
-#if CONFIG_SMP
 static unsigned long move(int curr_cpu, unsigned long allowed_mask, unsigned long now, int direction)
 {
 	int search_idle = 1;
@@ -264,9 +261,9 @@
 		set_ioapic_affinity(irq, 1 << entry->cpu);
 	}
 }
-#else /* !SMP */
+#else /* !CONFIG_IRQBALANCE */
 static inline void balance_irq(int irq) { }
-#endif
+#endif /* CONFIG_IRQBALANCE */
 
 /*
  * support for broken MP BIOSs, enables hand-redirection of PIRQ0-7 to