linux-kernel - [PATCH 3/4] Use the APIC to determine the hardware processor id

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Date:	Wed, 04 Apr 2007 17:56:37 +0900
From:	Fernando Luis Vázquez Cao 
	<fernando@....ntt.co.jp>
To:	akpm@...ux-foundation.org
Cc:	linux-kernel@...r.kernel.org, ak@...e.de, ebiederm@...ssion.com,
	horms@...ge.net.au, tony.luck@...el.com, vgoyal@...ibm.com
Subject: [PATCH 3/4] Use the APIC to determine the hardware processor id -
	x86_64

hard_smp_processor_id used to be just a macro that hard-coded
hard_smp_processor_id to 0 in the non SMP case.  When booting non SMP
kernels on hardware where the boot ioapic id is not 0 this turns out to
be a problem.  This is happens frequently in the case of kdump and once
in a great while in the case of real hardware.

Use the APIC to determine the hardware processor id in both UP and SMP
kernels to fix this issue.

Notice that hard_smp_processor_id is only used by SMP code or by code
that works
with apics so we do not need to handle the case when apics are not
present and hard_smp_processor_id should never be called there.

Signed-off-by: Fernando Luis Vazquez Cao <fernando@....ntt.co.jp>
---

diff -urNp linux-2.6.21-rc5-orig/include/asm-x86_64/smp.h linux-2.6.21-rc5/include/asm-x86_64/smp.h
--- linux-2.6.21-rc5-orig/include/asm-x86_64/smp.h	2007-04-04 15:57:31.000000000 +0900
+++ linux-2.6.21-rc5/include/asm-x86_64/smp.h	2007-04-04 16:25:52.000000000 +0900
@@ -59,12 +59,6 @@ static inline int num_booting_cpus(void)
 
 #define raw_smp_processor_id() read_pda(cpunumber)
 
-static inline int hard_smp_processor_id(void)
-{
-	/* we don't want to mark this access volatile - bad code generation */
-	return GET_APIC_ID(*(unsigned int *)(APIC_BASE+APIC_ID));
-}
-
 extern int __cpu_disable(void);
 extern void __cpu_die(unsigned int cpu);
 extern void prefill_possible_map(void);
@@ -73,10 +67,14 @@ extern unsigned __cpuinitdata disabled_c
 
 #define NO_PROC_ID		0xFF		/* No processor magic marker */
 
-#else /* CONFIG_SMP */
-#define hard_smp_processor_id() 0
 #endif /* CONFIG_SMP */
 
+static inline int hard_smp_processor_id(void)
+{
+	/* we don't want to mark this access volatile - bad code generation */
+	return GET_APIC_ID(*(unsigned int *)(APIC_BASE+APIC_ID));
+}
+
 /*
  * Some lowlevel functions might want to know about
  * the real APIC ID <-> CPU # mapping.


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