linux-kernel - Re: [PATCH 0/3] idle, Honor Hardware Disabled States

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Date:	Wed, 23 Mar 2016 19:50:51 -0400
From:	Prarit Bhargava <prarit@...hat.com>
To:	Len Brown <lenb@...nel.org>
CC:	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	X86 ML <x86@...nel.org>,
	"Peter Zijlstra (Intel)" <peterz@...radead.org>,
	Borislav Petkov <bp@...e.de>, Andi Kleen <ak@...ux.intel.com>,
	Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
	Dasaratharaman Chandramouli 
	<dasaratharaman.chandramouli@...el.com>,
	Linux PM list <linux-pm@...r.kernel.org>
Subject: Re: [PATCH 0/3] idle, Honor Hardware Disabled States



On 03/23/2016 04:05 PM, Len Brown wrote:
> This patch assumes that if a package state is disabled,
> the corresponding core state must be disabled.
> That assumption is false.
> Indeed, that is a very popular and useful configuration.
> 
> But even if that were not the case, this software is not necessary,
> since the hardware handles demotion "c-state clipping" automatically.
> 
> Yes, there is a case where a certain version of a certain processor
> has broken demotion, but this isn't the right fix for that.
> The right fix for that is here:
> 
> https://bugzilla.kernel.org/show_bug.cgi?id=109081

Len, should I rebase on top of this?  Would that work for you?

P.

> 
> and will be upstream shortly.
> 
> thanks,
> -Len
> 
> 
> 
> On Mon, Mar 21, 2016 at 8:49 AM, Prarit Bhargava <prarit@...hat.com> wrote:
>> Some Intel processors have cstates limited by MSR_PKG_CST_CONFIG_CONTROL
>> (0xE2), which specifies the lowest processor-specific C-state code name
>> (consuming the least power).  The intel_idle driver does not query this MSR to
>> see if states are limited by hardware.  In the case of the i7-6700HQ the value
>> of bits 3:0 on the MSR are 0x6, meaning that C9-SKL (0x7) and C10-SKL (0x8)
>> should have been disabled.
>>
>> This patch adds a limit field to the cpuidle_state struct to hold the
>> cstate encodings for each processor, and queries the values the values
>> to confirm support.
>>
>> After applying this patchset the system now boots and reports that
>> some states have been disabled:
>>
>> [root@...p40-125 ~]# dmesg | grep intel_idle
>> [    1.163367] intel_idle: MWAIT substates: 0x11142120
>> [    1.163368] intel_idle: v0.4 model 0x5E
>> [    1.163369] intel_idle: lapic_timer_reliable_states 0xffffffff
>> [    1.163370] intel_idle: state C9-SKL (0x7) is disabled.  Max Package limit is 0x6.
>> [    1.163371] intel_idle: state C10-SKL (0x8) is disabled.  Max Package limit is 0x6.
>>
>> Cc: x86@...nel.org
>> Cc: Len Brown <lenb@...nel.org>
>> Cc: "Peter Zijlstra (Intel)" <peterz@...radead.org>
>> Cc: Borislav Petkov <bp@...e.de>
>> Cc: Andi Kleen <ak@...ux.intel.com>
>> Cc: Alexander Shishkin <alexander.shishkin@...ux.intel.com>
>> Cc: Dasaratharaman Chandramouli <dasaratharaman.chandramouli@...el.com>
>> Cc: linux-pm@...r.kernel.org
>> Signed-off-by: Prarit Bhargava <prarit@...hat.com>
>>
>> Prarit Bhargava (3):
>>   idle, rename MSR_NHM_SNB_PKG_CST_CFG_CTL to
>>     MSR_PKG_CST_CONFIG_CONTROL
>>   intel_idle, Introduce cstate limits and fix hardware cstate disable
>>     value
>>   cpuidle, Prevent users from enabling cstates that are disabled in
>>     Hardware
>>
>>  arch/x86/include/asm/msr-index.h      |    2 +-
>>  drivers/cpuidle/governors/ladder.c    |    3 ++
>>  drivers/cpuidle/governors/menu.c      |    4 ++
>>  drivers/cpuidle/sysfs.c               |   34 +++++++++++-
>>  drivers/idle/intel_idle.c             |   93 ++++++++++++++++++++++++++++++++-
>>  include/linux/cpuidle.h               |   11 +++-
>>  tools/power/x86/turbostat/turbostat.8 |    2 +-
>>  tools/power/x86/turbostat/turbostat.c |   10 ++--
>>  8 files changed, 146 insertions(+), 13 deletions(-)
>>
>> --
>> 1.7.9.3
>>
> 
> 
>