[PATCH] skip sync_arb_IDs on P4/Xeon

[PATCH] skip sync_arb_IDs on P4/Xeon

[Martin Wilck]

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Hi,

I recently came across an Intel statement saying that the "INIT Level 
deassert" IPI used by sync_arb_IDs() (arch/i386/kernel/apic.c) should 
not be used on P4 and Xeon which don't have APIC bus arbitration anyway.

See Intel IA32 architecture software developers manual vol. 3, 8.6.1 
(p.8-23), 8.7 (p. 8.31).

The patch below skips the unsupported IPI on P4/Xeon.

The same thing should probably be done for x86_64.

Regards,
Martin

-- 
Martin Wilck                Phone: +49 5251 8 15113
Fujitsu Siemens Computers   Fax:   +49 5251 8 20409
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--- arch/i386/kernel/apic.c.orig	2004-10-04 14:54:27.000000000 +0200
+++ arch/i386/kernel/apic.c	2004-10-04 14:56:20.000000000 +0200
@@ -269,6 +269,9 @@ int __init verify_local_APIC(void)
 
 void __init sync_Arb_IDs(void)
 {
+	/* Unsupported on P4 - see Intel Dev. Manual Vol. 3, Ch. 8.6.1 */
+	if (boot_cpu_data.x86 == 15)
+		return;
 	/*
 	 * Wait for idle.
 	 */