linux-kernel - [PATCH 6/7] (Optional) implement smp_processor

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Date:	Fri, 22 Sep 2006 22:00:51 +1000
From:	Rusty Russell <rusty@...tcorp.com.au>
To:	Andi Kleen <ak@....de>
Cc:	lkml - Kernel Mailing List <linux-kernel@...r.kernel.org>,
	virtualization <virtualization@...ts.osdl.org>,
	Jeremy Fitzhardinge <jeremy@...p.org>
Subject: [PATCH 6/7] (Optional) implement smp_processor_id() as a per-cpu
	var

This implements smp_processor_id() as a per-cpu variable.  The generic
code expects it in thread_info still, so we can't remove it from
there, but reducing smp_processor_id() from 9 bytes/3 insns to 6
bytes/1 insn is a nice micro-optimization.

Signed-off-by: Rusty Russell <rusty@...tcorp.com.au>

Index: ak-pda-gs/arch/i386/kernel/smpboot.c
===================================================================
--- ak-pda-gs.orig/arch/i386/kernel/smpboot.c	2006-09-20 19:55:07.000000000 +1000
+++ ak-pda-gs/arch/i386/kernel/smpboot.c	2006-09-20 22:36:06.000000000 +1000
@@ -105,6 +105,9 @@
 DEFINE_PER_CPU(unsigned long, this_cpu_off);
 EXPORT_PER_CPU_SYMBOL(this_cpu_off);
 
+DEFINE_PER_CPU(u32, processor_id);
+EXPORT_PER_CPU_SYMBOL(processor_id);
+
 /*
  * Trampoline 80x86 program as an array.
  */
@@ -1355,6 +1358,7 @@
 	struct Xgt_desc_struct *cpu_gdt_descr = &per_cpu(cpu_gdt_descr, cpu);
 
 	per_cpu(this_cpu_off, cpu) = __per_cpu_offset[cpu];
+	per_cpu(processor_id, cpu) = cpu;
 	setup_percpu_descriptor(&gdt[GDT_ENTRY_PERCPU],	__per_cpu_offset[cpu]);
 	cpu_gdt_descr->address = (unsigned long)gdt;
 	cpu_gdt_descr->size = GDT_SIZE - 1;
Index: ak-pda-gs/include/asm-i386/smp.h
===================================================================
--- ak-pda-gs.orig/include/asm-i386/smp.h	2006-09-20 20:20:50.000000000 +1000
+++ ak-pda-gs/include/asm-i386/smp.h	2006-09-20 22:36:22.000000000 +1000
@@ -8,6 +8,7 @@
 #include <linux/kernel.h>
 #include <linux/threads.h>
 #include <linux/cpumask.h>
+#include <asm/percpu.h>
 #endif
 
 #ifdef CONFIG_X86_LOCAL_APIC
@@ -56,7 +57,8 @@
  * from the initial startup. We map APIC_BASE very early in page_setup(),
  * so this is correct in the x86 case.
  */
-#define raw_smp_processor_id() (current_thread_info()->cpu)
+DECLARE_PER_CPU(u32, processor_id);
+#define raw_smp_processor_id() x86_read_percpu(processor_id)
 
 extern cpumask_t cpu_callout_map;
 extern cpumask_t cpu_callin_map;
Index: ak-pda-gs/arch/i386/kernel/cpu/common.c
===================================================================
--- ak-pda-gs.orig/arch/i386/kernel/cpu/common.c	2006-09-20 21:28:28.000000000 +1000
+++ ak-pda-gs/arch/i386/kernel/cpu/common.c	2006-09-20 22:37:17.000000000 +1000
@@ -597,7 +597,7 @@
  */
 void __cpuinit cpu_init(void)
 {
-	int cpu = smp_processor_id();
+	unsigned int cpu = current->thread_info->cpu;
 	struct tss_struct * t = &per_cpu(init_tss, cpu);
 	struct thread_struct *thread = &current->thread;
 	struct desc_struct *gdt;

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