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Subject[PATCH 7/7] (Optional) implement current as a per-cpu var
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This implements current as a per-cpu variable.  The generic code
expects it in thread_info still, so I don't remove it from there, but
reducing current from 9 bytes/3 insns to 6 bytes/1 insn is a nice
micro-optimization.

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

Index: ak-fresh/arch/i386/kernel/setup.c
===================================================================
--- ak-fresh.orig/arch/i386/kernel/setup.c 2006-09-22 17:03:49.000000000 +1000
+++ ak-fresh/arch/i386/kernel/setup.c 2006-09-22 17:04:29.000000000 +1000
@@ -148,6 +148,9 @@

unsigned char __initdata boot_params[PARAM_SIZE];

+DEFINE_PER_CPU(struct task_struct *, current_task) = &init_task;
+EXPORT_PER_CPU_SYMBOL(current_task);
+
static struct resource data_resource = {
.name = "Kernel data",
.start = 0,
Index: ak-fresh/arch/i386/kernel/smpboot.c
===================================================================
--- ak-fresh.orig/arch/i386/kernel/smpboot.c 2006-09-22 17:04:18.000000000 +1000
+++ ak-fresh/arch/i386/kernel/smpboot.c 2006-09-22 17:04:29.000000000 +1000
@@ -598,12 +598,13 @@
* We don't actually need to load the full TSS,
* basically just the stack pointer and the eip.
*/
-
+ /* Can't use current until setup_percpu_for_this_cpu */
asm volatile(
"movl %0,%%esp\n\t"
"jmp *%1"
:
- :"r" (current->thread.esp),"r" (current->thread.eip));
+ :"r" (current_thread_info()->task->thread.esp),
+ "r" (current_thread_info()->task->thread.eip));
}

extern struct {
@@ -946,6 +947,8 @@
if (IS_ERR(idle))
panic("failed fork for CPU %d", cpu);
idle->thread.eip = (unsigned long) start_secondary;
+ per_cpu(current_task, cpu) = idle;
+
/* start_eip had better be page-aligned! */
start_eip = setup_trampoline();

Index: ak-fresh/include/asm-i386/current.h
===================================================================
--- ak-fresh.orig/include/asm-i386/current.h 2006-09-22 17:02:46.000000000 +1000
+++ ak-fresh/include/asm-i386/current.h 2006-09-22 17:04:29.000000000 +1000
@@ -1,15 +1,10 @@
#ifndef _I386_CURRENT_H
#define _I386_CURRENT_H

+#include <asm/percpu.h>
#include <linux/thread_info.h>

-struct task_struct;
-
-static __always_inline struct task_struct * get_current(void)
-{
- return current_thread_info()->task;
-}
-
-#define current get_current()
+DECLARE_PER_CPU(struct task_struct *, current_task);
+#define current x86_read_percpu(current_task)

#endif /* !(_I386_CURRENT_H) */
Index: ak-fresh/arch/i386/kernel/process.c
===================================================================
--- ak-fresh.orig/arch/i386/kernel/process.c 2006-09-22 17:02:46.000000000 +1000
+++ ak-fresh/arch/i386/kernel/process.c 2006-09-22 17:04:30.000000000 +1000
@@ -669,6 +669,7 @@
if (unlikely(prev->fs | next->fs))
loadsegment(fs, next->fs);

+ x86_write_percpu(current_task, next_p);

/*
* Restore IOPL if needed.
Index: ak-fresh/arch/i386/kernel/cpu/common.c
===================================================================
--- ak-fresh.orig/arch/i386/kernel/cpu/common.c 2006-09-22 17:04:18.000000000 +1000
+++ ak-fresh/arch/i386/kernel/cpu/common.c 2006-09-22 17:05:25.000000000 +1000
@@ -597,9 +597,10 @@
*/
void __cpuinit cpu_init(void)
{
- unsigned int cpu = current->thread_info->cpu;
+ /* Careful: can't use current() or smp_processor_id() yet! */
+ unsigned int cpu = current_thread_info()->cpu;
struct tss_struct * t = &per_cpu(init_tss, cpu);
- struct thread_struct *thread = &current->thread;
+ struct thread_struct *thread = &per_cpu(current_task, cpu)->thread;
struct desc_struct *gdt;
__u32 stk16_off = (__u32)&per_cpu(cpu_16bit_stack, cpu);

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