diff -u -r -N linux-2.6.0-test10/arch/i386/kernel/io_apic.c linux-2.6.0-test10-kai/arch/i386/kernel/io_apic.c
--- linux-2.6.0-test10/arch/i386/kernel/io_apic.c	2003-11-24 02:31:38.000000000 +0100
+++ linux-2.6.0-test10-kai/arch/i386/kernel/io_apic.c	2003-11-26 14:30:29.000000000 +0100
@@ -627,6 +627,16 @@
 		irqbalance_disabled = 1;
 		return 0;
 	}
+
+#ifdef CONFIG_X86_HT
+	/* On Hyper-Threading CPUs - if only one physical installed
+	   balance does not make sense */
+	if (cpu_has_ht && smp_num_siblings == 2 && num_online_cpus() == 2) {
+		irqbalance_disabled = 1;
+		return 0;
+	}
+#endif
+
 	/*
 	 * Enable physical balance only if more than 1 physical processor
 	 * is present