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[PATCH] i386: Convert PDA into the percpu section

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Currently x86 (similar to x84-64) has a special per-cpu structure
called "i386_pda" which can be easily and efficiently referenced via
the %fs register.  An ELF section is more flexible than a structure,
allowing any piece of code to use this area.  Indeed, such a section
already exists: the per-cpu area.

So this patch:
(1) Removes the PDA and uses per-cpu variables for each current member.
(2) Replaces the __KERNEL_PDA segment with __KERNEL_PERCPU.
(3) Creates a per-cpu mirror of __per_cpu_offset called this_cpu_off, which
    can be used to calculate addresses for this CPU's variables.
(4) Simplifies startup, because %fs doesn't need to be loaded with a
    special segment at early boot; it can be deferred until the first
    percpu area is allocated (or never for UP).

The result is less code and one less x86-specific concept.

Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>
Signed-off-by: Jeremy Fitzhardinge <jeremy@xensource.com>
Signed-off-by: Andi Kleen <ak@suse.de>
Cc: Andi Kleen <ak@suse.de>
This commit is contained in:
Jeremy Fitzhardinge
2007-05-02 19:27:16 +02:00
committed by Andi Kleen
parent 7a61d35d4b
commit 7c3576d261
17 changed files with 177 additions and 195 deletions
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12
arch/i386/kernel/process.c
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@@ -39,6 +39,7 @@
#include <linux/random.h>
#include <linux/personality.h>
#include <linux/tick.h>
#include <linux/percpu.h>
#include <asm/uaccess.h>
#include <asm/pgtable.h>
@@ -57,7 +58,6 @@
#include <asm/tlbflush.h>
#include <asm/cpu.h>
#include <asm/pda.h>
asmlinkage void ret_from_fork(void) __asm__("ret_from_fork");
@@ -66,6 +66,12 @@ static int hlt_counter;
unsigned long boot_option_idle_override = 0;
EXPORT_SYMBOL(boot_option_idle_override);
DEFINE_PER_CPU(struct task_struct *, current_task) = &init_task;
EXPORT_PER_CPU_SYMBOL(current_task);
DEFINE_PER_CPU(int, cpu_number);
EXPORT_PER_CPU_SYMBOL(cpu_number);
/*
* Return saved PC of a blocked thread.
*/
@@ -342,7 +348,7 @@ int kernel_thread(int (*fn)(void *), void * arg, unsigned long flags)
regs.xds = __USER_DS;
regs.xes = __USER_DS;
regs.xfs = __KERNEL_PDA;
regs.xfs = __KERNEL_PERCPU;
regs.orig_eax = -1;
regs.eip = (unsigned long) kernel_thread_helper;
regs.xcs = __KERNEL_CS | get_kernel_rpl();
@@ -711,7 +717,7 @@ struct task_struct fastcall * __switch_to(struct task_struct *prev_p, struct tas
if (prev->gs | next->gs)
loadsegment(gs, next->gs);
write_pda(pcurrent, next_p);
x86_write_percpu(current_task, next_p);
return prev_p;
}