oprofile: re-add force_arch_perfmon option

This re-adds the force_arch_perfmon option that was in the original
arch perfmon patchkit. Originally this was rejected in favour
of a generalized perfmon=name option, but it turned out implementing
the later in a reliable way is hard (and it would have been easy
to crash the kernel if a user gets it wrong)

But now Atom and Core i7 support being readded a user would
need to update their oprofile userland to beyond 0.9.4 to use oprofile again
on Atom or Core i7.

To avoid this problem readd the force_arch_perfmon option.
Signed-off-by: Andi Kleen <ak@linux.intel.com>
Signed-off-by: Robert Richter <robert.richter@amd.com>

1 files changed, 6 insertions, 0 deletions

diff --git a/arch/x86/oprofile/nmi_int.c b/arch/x86/oprofile/nmi_int.c
index 202864ad49a7..e5171c99e157 100644
--- a/arch/x86/oprofile/nmi_int.c
+++ b/arch/x86/oprofile/nmi_int.c
@@ -389,10 +389,16 @@ static int __init p4_init(char **cpu_type)
 	return 0;
 }
 
+int force_arch_perfmon;
+module_param(force_arch_perfmon, int, 0);
+
 static int __init ppro_init(char **cpu_type)
 {
 	__u8 cpu_model = boot_cpu_data.x86_model;
 
+	if (force_arch_perfmon && cpu_has_arch_perfmon)
+		return 0;
+
 	switch (cpu_model) {
 	case 0 ... 2:
 		*cpu_type = "i386/ppro";