optimization, cleanup: switch_to(3 parameter) => switch_to(2 parameter).

include/asm-i386/system.h

@@ -13,24 +13,23 @@ struct task_struct;	/* one of the stranger aspects of C forward declarations.. *
 extern void FASTCALL(__switch_to(struct task_struct *prev, struct task_struct *next));
 
 #define prepare_to_switch()	do { } while(0)
-#define switch_to(prev,next,last) do {					\
+
+#define switch_to(prev,next) do {					\
 	asm volatile("pushl %%esi\n\t"					\
 		     "pushl %%edi\n\t"					\
 		     "pushl %%ebp\n\t"					\
 		     "movl %%esp,%0\n\t"	/* save ESP */		\
-		     "movl %3,%%esp\n\t"	/* restore ESP */	\
+		     "movl %2,%%esp\n\t"	/* restore ESP */	\
 		     "movl $1f,%1\n\t"		/* save EIP */		\
-		     "pushl %4\n\t"		/* restore EIP */	\
+		     "pushl %3\n\t"		/* restore EIP */	\
 		     "jmp __switch_to\n"				\
 		     "1:\t"						\
 		     "popl %%ebp\n\t"					\
 		     "popl %%edi\n\t"					\
 		     "popl %%esi\n\t"					\
-		     :"=m" (prev->thread.esp),"=m" (prev->thread.eip),	\
-		      "=b" (last)					\
+		     :"=m" (prev->thread.esp),"=m" (prev->thread.eip)	\
 		     :"m" (next->thread.esp),"m" (next->thread.eip),	\
-		      "a" (prev), "d" (next),				\
-		      "b" (prev));					\
+		      "a" (prev), "d" (next));				\
 } while (0)
 
 #define _set_base(addr,base) do { unsigned long __pr; \

kernel/sched.c

@@ -435,17 +435,8 @@ static inline void context_switch(task_t *prev, task_t *next)
 		mmdrop(oldmm);
 	}
 
-	/*
-	 * Here we just switch the register state and the stack. There are
-	 * 3 processes affected by a context switch:
-	 *
-	 * prev ==> .... ==> (last => next)
-	 *
-	 * It's the 'much more previous' 'prev' that is on next's stack,
-	 * but prev is set to (the just run) 'last' process by switch_to().
-	 * This might sound slightly confusing but makes tons of sense.
-	 */
-	switch_to(prev, next, prev);
+	/* Here we just switch the register state and the stack. */
+	switch_to(prev, next);
 }
 
 unsigned long nr_running(void)