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

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=10914Signed-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
......@@ -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.
......
......@@ -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)
......
......@@ -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;
......
......@@ -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))
......
......@@ -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");
......
......@@ -764,6 +764,7 @@ prefetchw (const void *x)
extern unsigned long boot_option_idle_override;
extern unsigned long idle_halt;
extern unsigned long idle_nomwait;
#endif /* !__ASSEMBLY__ */
......
......@@ -728,6 +728,7 @@ extern void select_idle_routine(const struct cpuinfo_x86 *c);
extern unsigned long boot_option_idle_override;
extern unsigned long idle_halt;
extern unsigned long idle_nomwait;
extern void enable_sep_cpu(void);
extern int sysenter_setup(void);
......
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