[PATCH] OProfile: timer usage override

A patch mostly by Will Cohen, adding a parameter to OProfile to
over-ride use of the perfctr hardware. Useful for testing and
a host of other things.

Documentation/kernel-parameters.txt

@@ -652,6 +652,9 @@ running once the system is up.
 	opl3sa2=	[HW,OSS]
 			Format: <io>,<irq>,<dma>,<dma2>,<mss_io>,<mpu_io>,<ymode>,<loopback>[,<isapnp>,<multiple]
  
+	oprofile.timer=	[HW]
+			Use timer interrupt instead of performance counters
+
 	optcd=		[HW,CD]
 			Format: <io>
 

drivers/oprofile/oprof.c

@@ -11,6 +11,7 @@
 #include <linux/module.h>
 #include <linux/init.h>
 #include <linux/oprofile.h>
+#include <linux/moduleparam.h>
 #include <asm/semaphore.h>
 
 #include "oprof.h"
@@ -24,6 +25,12 @@ unsigned long oprofile_started;
 static unsigned long is_setup;
 static DECLARE_MUTEX(start_sem);
 
+/* timer
+   0 - use performance monitoring hardware if available
+   1 - use the timer int mechanism regardless
+ */
+static int timer = 0;
+
 int oprofile_setup(void)
 {
 	int err;
@@ -124,13 +131,16 @@ extern void timer_init(struct oprofile_operations ** ops);
 
 static int __init oprofile_init(void)
 {
-	int err;
+	int err = -ENODEV;
 
+	if (!timer) {
 		/* Architecture must fill in the interrupt ops and the
 		 * logical CPU type, or we can fall back to the timer
 		 * interrupt profiler.
 		 */
 		err = oprofile_arch_init(&oprofile_ops);
+	}
+
 	if (err == -ENODEV) {
 		timer_init(&oprofile_ops);
 		err = 0;
@@ -164,6 +174,9 @@ static void __exit oprofile_exit(void)
 module_init(oprofile_init);
 module_exit(oprofile_exit);
 
+module_param_named(timer, timer, int, 0644);
+MODULE_PARM_DESC(timer, "force use of timer interrupt");
+ 
 MODULE_LICENSE("GPL");
 MODULE_AUTHOR("John Levon <levon@movementarian.org>");
 MODULE_DESCRIPTION("OProfile system profiler");