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ACPI: skip checking BM_STS if the BIOS doesn't ask for it 

It turns out that there is a bit in the _CST for Intel FFH C3
that tells the OS if we should be checking BM_STS or not.

Linux has been unconditionally checking BM_STS.
If the chip-set is configured to enable BM_STS,
it can retard or completely prevent entry into
deep C-states -- as illustrated by turbostat:

http://userweb.kernel.org/~lenb/acpi/utils/pmtools/turbostat/

ref: Intel Processor Vendor-Specific ACPI Interface Specification
table 4 "_CST FFH GAS Field Encoding"
Bit 1: Set to 1 if OSPM should use Bus Master avoidance for this C-state

https://bugzilla.kernel.org/show_bug.cgi?id=15886

Signed-off-by: Len Brown <len.brown@intel.com>
This commit is contained in:
Len Brown 2010-07-22 16:54:27 -04:00
parent f4b23cc2d5
commit 718be4aaf3
3 changed files with 12 additions and 2 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

9
arch/x86/kernel/acpi/cstate.c
View File

@ -145,6 +145,15 @@ int acpi_processor_ffh_cstate_probe(unsigned int cpu,
percpu_entry->states[cx->index].eax = cx->address;
percpu_entry->states[cx->index].ecx = MWAIT_ECX_INTERRUPT_BREAK;
}
/*
* For _CST FFH on Intel, if GAS.access_size bit 1 is cleared,
* then we should skip checking BM_STS for this C-state.
* ref: "Intel Processor Vendor-Specific ACPI Interface Specification"
*/
if ((c->x86_vendor == X86_VENDOR_INTEL) && !(reg->access_size & 0x2))
cx->bm_sts_skip = 1;
return retval;
}
EXPORT_SYMBOL_GPL(acpi_processor_ffh_cstate_probe);

2
drivers/acpi/processor_idle.c
View File

@ -947,7 +947,7 @@ static int acpi_idle_enter_bm(struct cpuidle_device *dev,
if (acpi_idle_suspend)
return(acpi_idle_enter_c1(dev, state));
if (acpi_idle_bm_check()) {
if (!cx->bm_sts_skip && acpi_idle_bm_check()) {
if (dev->safe_state) {
dev->last_state = dev->safe_state;
return dev->safe_state->enter(dev, dev->safe_state);

3
include/acpi/processor.h
View File

@ -48,7 +48,7 @@ struct acpi_power_register {
u8 space_id;
u8 bit_width;
u8 bit_offset;
u8 reserved;
u8 access_size;
u64 address;
} __attribute__ ((packed));
@ -63,6 +63,7 @@ struct acpi_processor_cx {
u32 power;
u32 usage;
u64 time;
u8 bm_sts_skip;
char desc[ACPI_CX_DESC_LEN];
};