ACPI : Create "idle=nomwait" bootparam

"idle=nomwait" disables the use of the MWAIT
instruction from both C1 (C1_FFH) and deeper (C2C3_FFH)
C-states.

When MWAIT is unavailable, the BIOS and OS generally
negotiate to use the HALT instruction for C1,
and use IO accesses for deeper C-states.

This option is useful for power and performance
comparisons, and also to work around BIOS bugs
where broken MWAIT support is advertised.

http://bugzilla.kernel.org/show_bug.cgi?id=10807
http://bugzilla.kernel.org/show_bug.cgi?id=10914

Signed-off-by: Zhao Yakui <yakui.zhao@intel.com>
Signed-off-by: Li Shaohua <shaohua.li@intel.com>
Signed-off-by: Len Brown <len.brown@intel.com>
Signed-off-by: Andi Kleen <ak@linux.intel.com>

1 files changed, 2 insertions, 1 deletions

diff --git a/Documentation/kernel-parameters.txt b/Documentation/kernel-parameters.txt
index 65db7f4711aa..5e497d16fb51 100644
--- a/Documentation/kernel-parameters.txt
+++ b/Documentation/kernel-parameters.txt
@@ -818,7 +818,7 @@ and is between 256 and 4096 characters. It is defined in the file
                         See Documentation/ide/ide.txt.
 
         idle=           [X86]
-                        Format: idle=poll or idle=mwait, idle=halt
+                        Format: idle=poll or idle=mwait, idle=halt, idle=nomwait
                         Poll forces a polling idle loop that can slightly improves the performance
                         of waking up a idle CPU, but will use a lot of power and make the system
                         run hot. Not recommended.
@@ -828,6 +828,7 @@ and is between 256 and 4096 characters. It is defined in the file
                         as idle=poll.
                         idle=halt. Halt is forced to be used for CPU idle.
                         In such case C2/C3 won't be used again.
+                        idle=nomwait. Disable mwait for CPU C-states
 
         ide-pci-generic.all-generic-ide [HW] (E)IDE subsystem
                         Claim all unknown PCI IDE storage controllers.