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/Documentation/kernel-parameters.txt b/Documentation/kernel-parameters.txt
index 90b3924071b..9b9566bf330 100644
--- a/Documentation/kernel-parameters.txt
+++ b/Documentation/kernel-parameters.txt
@@ -1650,6 +1650,12 @@ and is between 256 and 4096 characters. It is defined in the file
 	oprofile.timer=	[HW]
 			Use timer interrupt instead of performance counters
 
+	oprofile.force_arch_perfmon=1	[X86]
+			Force use of architectural perfmon instead of
+			the CPU specific event set.
+			This might be useful if you have older oprofile
+			userland or if you want common events over Intel CPUs.
+
 	osst=		[HW,SCSI] SCSI Tape Driver
 			Format: <buffer_size>,<write_threshold>
 			See also Documentation/scsi/st.txt.