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SubjectRe: [PATCH 2.6.{32, 33, 34}.stable] ACPI: skip checking BM_STS if the BIOS doesn't ask for it
On Mon 2010-07-26 19:51:29, Len Brown wrote:
> From: Len Brown <len.brown@intel.com>
>
> upstream 718be4aaf3613cf7c2d097f925abc3d3553c0605
>
> 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 is better than cpu whitelist. Thanks!


> ---
>
> this backport applies cleanly to 2.6.32.y.
> It applies w/ a small offset to 2.6.33.y and 2.34.y
>
>
> arch/x86/kernel/acpi/cstate.c | 9 +++++++++
> drivers/acpi/processor_idle.c | 2 +-
> include/acpi/processor.h | 3 ++-
> 3 files changed, 12 insertions(+), 2 deletions(-)
>
> Index: linux-2.6.32.y/arch/x86/kernel/acpi/cstate.c
> ===================================================================
> --- linux-2.6.32.y.orig/arch/x86/kernel/acpi/cstate.c
> +++ linux-2.6.32.y/arch/x86/kernel/acpi/cstate.c
> @@ -145,6 +145,15 @@ int acpi_processor_ffh_cstate_probe(unsi
> 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);
> Index: linux-2.6.32.y/drivers/acpi/processor_idle.c
> ===================================================================
> --- linux-2.6.32.y.orig/drivers/acpi/processor_idle.c
> +++ linux-2.6.32.y/drivers/acpi/processor_idle.c
> @@ -962,7 +962,7 @@ static int acpi_idle_enter_bm(struct cpu
> 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);
> Index: linux-2.6.32.y/include/acpi/processor.h
> ===================================================================
> --- linux-2.6.32.y.orig/include/acpi/processor.h
> +++ linux-2.6.32.y/include/acpi/processor.h
> @@ -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));
>
> @@ -74,6 +74,7 @@ struct acpi_processor_cx {
> u32 power;
> u32 usage;
> u64 time;
> + u8 bm_sts_skip;
> struct acpi_processor_cx_policy promotion;
> struct acpi_processor_cx_policy demotion;
> char desc[ACPI_CX_DESC_LEN];
> --
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