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

[Rusty Russell]

On Fri, 2006-09-22 at 22:01 +1000, Rusty Russell wrote:
> This implements current as a per-cpu variable.

Again, revised for updated 5/7: we no longer need to avoid using current
early on.

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@xxxxxxxxxxxxxxx>

Index: ak-fresh/arch/i386/kernel/setup.c
===================================================================
--- ak-fresh.orig/arch/i386/kernel/setup.c	2006-09-25 15:02:33.000000000 +1000
+++ ak-fresh/arch/i386/kernel/setup.c	2006-09-25 15:06:31.000000000 +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	2006-09-25 15:02:51.000000000 +1000
+++ ak-fresh/arch/i386/kernel/smpboot.c	2006-09-25 15:06:31.000000000 +1000
@@ -972,6 +972,7 @@
 	if (IS_ERR(idle))
 		panic("failed fork for CPU %d", cpu);
 	idle->thread.eip = (unsigned long) start_secondary;
+	per_cpu(current_task, cpu) = idle;
 
  	setup_percpu(cpu);
  	booting_cpu_gdt_desc_ptr = &per_cpu(cpu_gdt_descr, cpu);
Index: ak-fresh/include/asm-i386/current.h
===================================================================
--- ak-fresh.orig/include/asm-i386/current.h	2006-09-25 15:02:33.000000000 +1000
+++ ak-fresh/include/asm-i386/current.h	2006-09-25 15:06:31.000000000 +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	2006-09-25 15:02:33.000000000 +1000
+++ ak-fresh/arch/i386/kernel/process.c	2006-09-25 15:06:31.000000000 +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.

-- 
Help! Save Australia from the worst of the DMCA: http://linux.org.au/law

-
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/