[PATCH/RFC v2 4/6] stop_machine: special case for one cpu

[Heiko Carstens <heiko.carstens@de.ibm.com>]

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From: Heiko Carstens <heiko.carstens@de.ibm.com>

If only one cpu is online we might as well use the non-smp variant of
stop_machine which should be much faster since no scheduling is needed.

Signed-off-by: Heiko Carstens <heiko.carstens@de.ibm.com>
---
 include/linux/stop_machine.h |   16 +++++++++++-----
 kernel/stop_machine.c        |    3 +++
 2 files changed, 14 insertions(+), 5 deletions(-)

Index: linux-2.6/include/linux/stop_machine.h
===================================================================
--- linux-2.6.orig/include/linux/stop_machine.h
+++ linux-2.6/include/linux/stop_machine.h
@@ -8,6 +8,16 @@
 #include <linux/cpumask.h>
 #include <asm/system.h>
 
+static inline int stop_machine_simple(int (*fn)(void *), void *data,
+				      const cpumask_t *cpus)
+{
+	int ret;
+	local_irq_disable();
+	ret = fn(data);
+	local_irq_enable();
+	return ret;
+}
+
 #if defined(CONFIG_STOP_MACHINE) && defined(CONFIG_SMP)
 
 /**
@@ -40,11 +50,7 @@ int __stop_machine(int (*fn)(void *), vo
 static inline int stop_machine(int (*fn)(void *), void *data,
 			       const cpumask_t *cpus)
 {
-	int ret;
-	local_irq_disable();
-	ret = fn(data);
-	local_irq_enable();
-	return ret;
+	return stop_machine_simple(fn, data, cpus);
 }
 #endif /* CONFIG_SMP */
 #endif /* _LINUX_STOP_MACHINE */
Index: linux-2.6/kernel/stop_machine.c
===================================================================
--- linux-2.6.orig/kernel/stop_machine.c
+++ linux-2.6/kernel/stop_machine.c
@@ -111,6 +111,9 @@ int __stop_machine(int (*fn)(void *), vo
 	struct work_struct *sm_work;
 	int i;
 
+	if (num_online_cpus() == 1)
+		return stop_machine_simple(fn, data, cpus);
+
 	/* Set up initial state. */
 	mutex_lock(&lock);
 	num_threads = num_online_cpus();

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