--- linux/arch/i386/kernel/io_apic.c.orig	2004-05-10 14:08:00.000000000 +0200
+++ linux/arch/i386/kernel/io_apic.c	2004-05-10 14:12:17.000000000 +0200
@@ -2159,6 +2159,10 @@
 {
 	int pin1, pin2;
 	int vector;
+	unsigned int ver;
+
+	ver = apic_read(APIC_LVR);
+	ver = GET_APIC_VERSION(ver);
 
 	/*
 	 * get/set the timer IRQ vector:
@@ -2172,11 +2176,15 @@
 	 * mode for the 8259A whenever interrupts are routed
 	 * through I/O APICs.  Also IRQ0 has to be enabled in
 	 * the 8259A which implies the virtual wire has to be
-	 * disabled in the local APIC.
+	 * disabled in the local APIC. Finally timer interrupts
+	 * need to be acknowledged manually in the 8259A for
+	 * do_slow_timeoffset() and for the i82489DX when using
+	 * the NMI watchdog.
 	 */
 	apic_write_around(APIC_LVT0, APIC_LVT_MASKED | APIC_DM_EXTINT);
 	init_8259A(1);
-	timer_ack = 1;
+	timer_ack = !cpu_has_tsc;
+	timer_ack |= nmi_watchdog == NMI_IO_APIC && !APIC_INTEGRATED(ver);
 	enable_8259A_irq(0);
 
 	pin1 = find_isa_irq_pin(0, mp_INT);
@@ -2194,7 +2202,8 @@
 				disable_8259A_irq(0);
 				setup_nmi();
 				enable_8259A_irq(0);
-				check_nmi_watchdog();
+				if (check_nmi_watchdog() < 0)
+					timer_ack = !cpu_has_tsc;
 			}
 			return;
 		}
@@ -2217,7 +2226,8 @@
 				add_pin_to_irq(0, 0, pin2);
 			if (nmi_watchdog == NMI_IO_APIC) {
 				setup_nmi();
-				check_nmi_watchdog();
+				if (check_nmi_watchdog() < 0)
+					timer_ack = !cpu_has_tsc;
 			}
 			return;
 		}