oprofile/x86: add comment to counter-in-use warning

Currently, oprofile fails silently on platforms where a non-OS entity
such as the system firmware "enables" and uses a performance
counter. There is a warning in the code for this case.

The warning indicates an already running counter. If oprofile doesn't
collect data, then try using a different performance counter on your
platform to monitor the desired event. Delete the counter from the
desired event by editing the

 /usr/share/oprofile/<cpu_type>/<cpu>/events

file. If the event cannot be monitored by any other counter, contact
your hardware or BIOS vendor.

Cc: Shashi Belur <shashi-kiran.belur@hp.com>
Cc: Tony Jones <tonyj@suse.de>
Signed-off-by: Naga Chumbalkar <nagananda.chumbalkar@hp.com>
Signed-off-by: Robert Richter <robert.richter@amd.com>

arch/x86/oprofile/op_x86_model.h

@@ -59,6 +59,15 @@ struct op_counter_config;
 
 static inline void op_x86_warn_in_use(int counter)
 {
+	/*
+	 * The warning indicates an already running counter. If
+	 * oprofile doesn't collect data, then try using a different
+	 * performance counter on your platform to monitor the desired
+	 * event. Delete counter #%d from the desired event by editing
+	 * the /usr/share/oprofile/%s/<cpu>/events file. If the event
+	 * cannot be monitored by any other counter, contact your
+	 * hardware or BIOS vendor.
+	 */
 	pr_warning("oprofile: counter #%d on cpu #%d may already be used\n",
 		   counter, smp_processor_id());
 }