Name: Make current an attribute pure function
Author: Rusty Russell
Status: Experimental

"current" can be considered constant in all cases it is used except in
schedule where it actually changes.  Can we convince gcc to generate
better code?

Index: linux-2.6.10-rc2-bk9-Misc/include/asm-i386/current.h
===================================================================
--- linux-2.6.10-rc2-bk9-Misc.orig/include/asm-i386/current.h	2003-09-21 17:34:17.000000000 +1000
+++ linux-2.6.10-rc2-bk9-Misc/include/asm-i386/current.h	2004-11-26 14:28:32.990386064 +1100
@@ -5,10 +5,7 @@
 
 struct task_struct;
 
-static inline struct task_struct * get_current(void)
-{
-	return current_thread_info()->task;
-}
+struct task_struct *get_current(void) __attribute__((pure));
  
 #define current get_current()
 
Index: linux-2.6.10-rc2-bk9-Misc/kernel/sched.c
===================================================================
--- linux-2.6.10-rc2-bk9-Misc.orig/kernel/sched.c	2004-11-26 11:48:28.000000000 +1100
+++ linux-2.6.10-rc2-bk9-Misc/kernel/sched.c	2004-11-26 14:30:16.041719880 +1100
@@ -2292,7 +2292,6 @@
 void scheduler_tick(int user_ticks, int sys_ticks)
 {
 	int cpu = smp_processor_id();
-	struct cpu_usage_stat *cpustat = &kstat_this_cpu.cpustat;
 	runqueue_t *rq = this_rq();
 	task_t *p = current;
 
@@ -2303,28 +2302,28 @@
 
 	/* note: this timer irq context must be accounted for as well */
 	if (hardirq_count() - HARDIRQ_OFFSET) {
-		cpustat->irq += sys_ticks;
+		kstat_this_cpu.cpustat.irq += sys_ticks;
 		sys_ticks = 0;
 	} else if (softirq_count()) {
-		cpustat->softirq += sys_ticks;
+		kstat_this_cpu.cpustat.softirq += sys_ticks;
 		sys_ticks = 0;
 	}
 
 	if (p == rq->idle) {
 		if (atomic_read(&rq->nr_iowait) > 0)
-			cpustat->iowait += sys_ticks;
+			kstat_this_cpu.cpustat.iowait += sys_ticks;
 		else
-			cpustat->idle += sys_ticks;
+			kstat_this_cpu.cpustat.idle += sys_ticks;
 		if (wake_priority_sleeper(rq))
 			goto out;
 		rebalance_tick(cpu, rq, SCHED_IDLE);
 		return;
 	}
 	if (TASK_NICE(p) > 0)
-		cpustat->nice += user_ticks;
+		kstat_this_cpu.cpustat.nice += user_ticks;
 	else
-		cpustat->user += user_ticks;
-	cpustat->system += sys_ticks;
+		kstat_this_cpu.cpustat.user += user_ticks;
+	kstat_this_cpu.cpustat.system += sys_ticks;
 
 	/* Task might have expired already, but not scheduled off yet */
 	if (p->array != rq->active) {
Index: linux-2.6.10-rc2-bk9-Misc/arch/i386/kernel/process.c
===================================================================
--- linux-2.6.10-rc2-bk9-Misc.orig/arch/i386/kernel/process.c	2004-11-16 15:29:02.000000000 +1100
+++ linux-2.6.10-rc2-bk9-Misc/arch/i386/kernel/process.c	2004-11-26 14:28:32.990386064 +1100
@@ -810,3 +810,7 @@
 	return 0;
 }
 
+struct task_struct *get_current(void)
+{
+	return current_thread_info()->task;
+}