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    Subject[PATCH 7/7] (Optional) implement current as a per-cpu var
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    Date
    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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