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Commit da5e09a1 authored by Zhao Yakui's avatar Zhao Yakui Committed by Andi Kleen
Browse files

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: default avatarZhao Yakui <yakui.zhao@intel.com>
Signed-off-by: default avatarLi Shaohua <shaohua.li@intel.com>
Signed-off-by: default avatarLen Brown <len.brown@intel.com>
Signed-off-by: default avatarAndi Kleen <ak@linux.intel.com>
parent c1e3b377

Documentation/kernel-parameters.txt

+2 −1
Original line number Diff line number Diff line
@@ -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.

arch/ia64/kernel/process.c

+2 −0
Original line number Diff line number Diff line
@@ -57,6 +57,8 @@ unsigned long boot_option_idle_override = 0; 
EXPORT_SYMBOL(boot_option_idle_override);

unsigned long idle_halt;

EXPORT_SYMBOL(idle_halt);

unsigned long idle_nomwait;

EXPORT_SYMBOL(idle_nomwait);



void

ia64_do_show_stack (struct unw_frame_info *info, void *arg)

arch/x86/kernel/process.c

+11 −0
Original line number Diff line number Diff line
@@ -11,6 +11,8 @@ 


unsigned long idle_halt;

EXPORT_SYMBOL(idle_halt);

unsigned long idle_nomwait;

EXPORT_SYMBOL(idle_nomwait);



struct kmem_cache *task_xstate_cachep;
@@ -340,6 +342,15 @@ static int __init idle_setup(char *str) 
		pm_idle = default_idle;

		idle_halt = 1;

		return 0;

	} else if (!strcmp(str, "nomwait")) {

		/*

		 * If the boot option of "idle=nomwait" is added,

		 * it means that mwait will be disabled for CPU C2/C3

		 * states. In such case it won't touch the variable

		 * of boot_option_idle_override.

		 */

		idle_nomwait = 1;

		return 0;

	} else

		return -1;

drivers/acpi/processor_core.c

+13 −0
Original line number Diff line number Diff line
@@ -265,7 +265,20 @@ static int acpi_processor_set_pdc(struct acpi_processor *pr) 


	if (!pdc_in)

		return status;

	if (idle_nomwait) {

		/*

		 * If mwait is disabled for CPU C-states, the C2C3_FFH access

		 * mode will be disabled in the parameter of _PDC object.

		 * Of course C1_FFH access mode will also be disabled.

		 */

		union acpi_object *obj;

		u32 *buffer = NULL;



		obj = pdc_in->pointer;

		buffer = (u32 *)(obj->buffer.pointer);

		buffer[2] &= ~(ACPI_PDC_C_C2C3_FFH | ACPI_PDC_C_C1_FFH);



	}

	status = acpi_evaluate_object(pr->handle, "_PDC", pdc_in, NULL);



	if (ACPI_FAILURE(status))

drivers/acpi/processor_idle.c

+5 −1
Original line number Diff line number Diff line
@@ -957,13 +957,17 @@ static int acpi_processor_get_power_info_cst(struct acpi_processor *pr) 
			} else {

				continue;

			}

			if (cx.type == ACPI_STATE_C1 && idle_halt) {

			if (cx.type == ACPI_STATE_C1 &&

					(idle_halt || idle_nomwait)) {

				/*

				 * In most cases the C1 space_id obtained from

				 * _CST object is FIXED_HARDWARE access mode.

				 * But when the option of idle=halt is added,

				 * the entry_method type should be changed from

				 * CSTATE_FFH to CSTATE_HALT.

				 * When the option of idle=nomwait is added,

				 * the C1 entry_method type should be

				 * CSTATE_HALT.

				 */

				cx.entry_method = ACPI_CSTATE_HALT;

				snprintf(cx.desc, ACPI_CX_DESC_LEN, "ACPI HLT");