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Message-ID: <4CFDF785.7010401@kernel.org>
Date: Tue, 07 Dec 2010 00:59:49 -0800
From: Yinghai Lu <yinghai@...nel.org>
To: mingo@...hat.com, hpa@...or.com, tglx@...utronix.de
CC: linux-kernel@...r.kernel.org, bigeasy@...utronix.de
Subject: [PATCH -v2] x86, ioapic: Don't write io_apic ID if it is not changed
For 32bit mptable path, setup_ids_from_mpc() always write io apic id
register, even there is no change needed.
So try to do that when they are different bewteen reading out and mptable
-v2: update to recent setup_ioapic_ids_from_mpc() split..
Signed-off-by: Yinghai Lu <yinghai@...nel.org>
---
arch/x86/kernel/apic/io_apic.c | 7 +++++--
1 file changed, 5 insertions(+), 2 deletions(-)
Index: linux-2.6/arch/x86/kernel/apic/io_apic.c
===================================================================
--- linux-2.6.orig/arch/x86/kernel/apic/io_apic.c
+++ linux-2.6/arch/x86/kernel/apic/io_apic.c
@@ -2006,9 +2006,12 @@ void __init setup_ioapic_ids_from_mpc_no
= mp_ioapics[apic_id].apicid;
/*
- * Read the right value from the MPC table and
- * write it into the ID register.
+ * Update the ID register according to the right value from
+ * the MPC table if they are different.
*/
+ if (mp_ioapics[apic_id].apicid == reg_00.bits.ID)
+ continue;
+
apic_printk(APIC_VERBOSE, KERN_INFO
"...changing IO-APIC physical APIC ID to %d ...",
mp_ioapics[apic_id].apicid);
--
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