Re: [PATCH 6/7] (Optional) implement smp_processor_id() as aper-cpu var

[Rusty Russell]

On Fri, 2006-09-22 at 22:00 +1000, Rusty Russell wrote:
> This implements smp_processor_id() as a per-cpu variable.

Updated for revised 5/7: we no longer need to avoid using
smp_processor_id() in cpu_init.

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@xxxxxxxxxxxxxxx>

Index: ak-fresh/arch/i386/kernel/smpboot.c
===================================================================
--- ak-fresh.orig/arch/i386/kernel/smpboot.c	2006-09-25 14:49:05.000000000 +1000
+++ ak-fresh/arch/i386/kernel/smpboot.c	2006-09-25 15:02:51.000000000 +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.
  */
@@ -939,6 +942,7 @@
 	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;
@@ -1361,6 +1365,7 @@
 	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-fresh/include/asm-i386/smp.h
===================================================================
--- ak-fresh.orig/include/asm-i386/smp.h	2006-09-25 14:49:05.000000000 +1000
+++ ak-fresh/include/asm-i386/smp.h	2006-09-25 14:52:05.000000000 +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;

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