Name: on_one_cpu function
Author: Rusty Russell
Status: Booted on 2.6.5

Similar to on_each_cpu, this implements on_one_cpu.  For archs which
don't do it natively, it's implemented in terms of smp_call_function().

diff -urpN --exclude TAGS -X /home/rusty/devel/kernel/kernel-patches/current-dontdiff --minimal .21074-linux-2.6.5/include/linux/smp.h .21074-linux-2.6.5.updated/include/linux/smp.h
diff -urpN --exclude TAGS -X /home/rusty/devel/kernel/kernel-patches/current-dontdiff --minimal .23974-linux-2.6.7-rc2/include/linux/smp.h .23974-linux-2.6.7-rc2.updated/include/linux/smp.h
--- .23974-linux-2.6.7-rc2/include/linux/smp.h	2004-03-12 07:57:26.000000000 +1100
+++ .23974-linux-2.6.7-rc2.updated/include/linux/smp.h	2004-05-31 12:05:43.000000000 +1000
@@ -8,6 +8,10 @@
 
 #include <linux/config.h>
 
+#define get_cpu()		({ preempt_disable(); smp_processor_id(); })
+#define put_cpu()		preempt_enable()
+#define put_cpu_no_resched()	preempt_enable_no_resched()
+
 #ifdef CONFIG_SMP
 
 #include <linux/preempt.h>
@@ -69,6 +73,11 @@ static inline int on_each_cpu(void (*fun
 	return ret;
 }
 
+#ifndef __HAVE_ARCH_ON_ONE_CPU
+extern int on_one_cpu(unsigned cpu, void (*func)(void *info), void *info);
+#endif
+
+
 /*
  * True once the per process idle is forked
  */
@@ -101,14 +110,11 @@ void smp_prepare_boot_cpu(void);
 #define smp_threads_ready			1
 #define smp_call_function(func,info,retry,wait)	({ 0; })
 #define on_each_cpu(func,info,retry,wait)	({ func(info); 0; })
+#define on_one_cpu(cpu,func,info)		({ func(info); 0; })
 static inline void smp_send_reschedule(int cpu) { }
 #define num_booting_cpus()			1
 #define smp_prepare_boot_cpu()			do {} while (0)
 
 #endif /* !SMP */
 
-#define get_cpu()		({ preempt_disable(); smp_processor_id(); })
-#define put_cpu()		preempt_enable()
-#define put_cpu_no_resched()	preempt_enable_no_resched()
-
 #endif /* __LINUX_SMP_H */
diff -urpN --exclude TAGS -X /home/rusty/devel/kernel/kernel-patches/current-dontdiff --minimal .23974-linux-2.6.7-rc2/kernel/sched.c .23974-linux-2.6.7-rc2.updated/kernel/sched.c
--- .23974-linux-2.6.7-rc2/kernel/sched.c	2004-05-31 09:57:40.000000000 +1000
+++ .23974-linux-2.6.7-rc2.updated/kernel/sched.c	2004-05-31 12:06:40.000000000 +1000
@@ -671,7 +671,39 @@ static inline unsigned long target_load(
 	return max(rq->cpu_load, load_now);
 }
 
-#endif
+#ifndef __HAVE_ARCH_ON_ONE_CPU
+struct which_cpu
+{
+	unsigned int cpu;
+	void (*func)(void *info);
+	void *info;
+};
+
+static void maybe_on_cpu(void *_which)
+{
+	struct which_cpu *which = _which;
+
+	if (smp_processor_id() == which->cpu)
+		which->func(which->info);
+}
+
+static inline int on_one_cpu(unsigned cpu,
+			     void (*func)(void *info), void *info)
+{
+	int ret;
+
+	if (cpu == get_cpu()) {
+		func(info);
+		ret = 0;
+	} else {
+		struct which_cpu which = { cpu, func, info };
+		ret = smp_call_function(maybe_on_cpu, &which, 1, 1);
+	}
+	put_cpu();
+	return ret;
+}
+#endif /* __HAVE_ARCH_ON_ONE_CPU */
+#endif /* CONFIG_SMP */
 
 /*
  * wake_idle() is useful especially on SMT architectures to wake a