linux-kernel - Re: [PATCH 2.6.{32, 33, 34}.stable] ACPI: skip checking BM

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Message-ID: <20100803065403.GD3344@ucw.cz>
Date:	Tue, 3 Aug 2010 08:54:03 +0200
From:	Pavel Machek <pavel@....cz>
To:	Len Brown <lenb@...nel.org>
Cc:	stable@...nel.org,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	linux-acpi@...r.kernel.org
Subject: Re: [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@...el.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@...el.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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