linux-kernel - Re: [PATCH 2/2 V8] intel_pstate: add kernel parameter to force loading.

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Date:	Sat, 06 Dec 2014 12:36:34 -0500
From:	Linda Knippers <linda.knippers@...com>
To:	ethan <ethan.kernel@...il.com>
CC:	Ethan Zhao <ethan.zhao@...cle.com>,
	"dirk.j.brandewie@...el.com" <dirk.j.brandewie@...el.com>,
	"kristen@...ux.intel.com" <kristen@...ux.intel.com>,
	"viresh.kumar@...aro.org" <viresh.kumar@...aro.org>,
	"rjw@...ysocki.net" <rjw@...ysocki.net>,
	"corbet@....net" <corbet@....net>,
	"linux-doc@...r.kernel.org" <linux-doc@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-pm@...r.kernel.org" <linux-pm@...r.kernel.org>,
	"alexey.kodanev@...cle.com" <alexey.kodanev@...cle.com>
Subject: Re: [PATCH 2/2 V8] intel_pstate: add kernel parameter to force loading.

On 12/5/2014 9:16 PM, ethan wrote:
> Linda，
> 
>> 在 2014年12月6日，00:09，Linda Knippers <linda.knippers@...com> 写道：
>>
>>> On 12/5/2014 4:40 AM, Ethan Zhao wrote:
>>> To force loading on Oracle Sun X86 servers, provide one kernel command line
>>> parameter
>>>
>>>  intel_pstate = force
>>>
>>> For those who be aware of the risk of no power capping capabily working and
>>> try to get better performance with this driver.
>>>
>>> Signed-off-by: Ethan Zhao <ethan.zhao@...cle.com>
>>> Tested-by: Alexey Kodanev <alexey.kodanev@...cle.com>
>>> ---
>>> v2: change to hardware vendor specific naming parameter.
>>> v4: refine code and doc.
>>> v5&v6: fix a typo in doc.
>>> v7: change enum PCC to PPC.
>>> v8: change the name of kernel command line parameter to generic one.
>>>
>>> Documentation/kernel-parameters.txt | 5 +++++
>>> drivers/cpufreq/intel_pstate.c      | 6 +++++-
>>> 2 files changed, 10 insertions(+), 1 deletion(-)
>>>
>>> diff --git a/Documentation/kernel-parameters.txt b/Documentation/kernel-parameters.txt
>>> index 479f332..7d0983e 100644
>>> --- a/Documentation/kernel-parameters.txt
>>> +++ b/Documentation/kernel-parameters.txt
>>> @@ -1446,6 +1446,11 @@ bytes respectively. Such letter suffixes can also be entirely omitted.
>>>               disable
>>>                 Do not enable intel_pstate as the default
>>>                 scaling driver for the supported processors
>>> +               force
>>> +             Enable intel_pstate on systems where it may cause problems to
>>> +             happen due to conflicts with platform firmware attempting to
>>> +             drive P-states by itself in certain situations (for thermal 
>>> +             control or power capping in general or other purposes).
>>
>> I suggest something like:
>>            Enable intel_pstate on systems that prohibit it by
>>            default in favor of acpi-cpufreq.  Forcing the
>>            intel_pstate driver instead of acpi-cpufreq may disable
>>            platform features, such as thermal controls and power
>>            capping, that rely on ACPI p-state information being
>                                                          P-States 
>>             Used by the OS and therefore should be used with care.
>                Indicated to OSPM                                                   caution 
>>            This option does not work with processors that aren't
>>            supported by the intel_pstate driver or on platforms
>>            that use pcc-cpufreq instead of acpi-cpufreq.
>>
>> Maybe this is too specific but I believe it is accurate.  Comments?
>>
> 
> Looks better to me, except some words commented. 

Your suggestions look fine to me.

-- ljk
> 
> Thanks,
> Ethan
>> -- ljk
>>
>>>
>>>    intremap=    [X86-64, Intel-IOMMU]
>>>            on    enable Interrupt Remapping (default)
>>> diff --git a/drivers/cpufreq/intel_pstate.c b/drivers/cpufreq/intel_pstate.c
>>> index 1bb62ca..2654e13 100644
>>> --- a/drivers/cpufreq/intel_pstate.c
>>> +++ b/drivers/cpufreq/intel_pstate.c
>>> @@ -866,6 +866,7 @@ static struct cpufreq_driver intel_pstate_driver = {
>>> };
>>>
>>> static int __initdata no_load;
>>> +static unsigned int  force_load;
>>>
>>> static int intel_pstate_msrs_not_valid(void)
>>> {
>>> @@ -1003,7 +1004,8 @@ static bool intel_pstate_platform_pwr_mgmt_exists(void)
>>>            case PSS:
>>>                return intel_pstate_no_acpi_pss();
>>>            case PPC:
>>> -                return intel_pstate_has_acpi_ppc();
>>> +                return intel_pstate_has_acpi_ppc() &&
>>> +                    (!force_load);
>>>            }
>>>    }
>>>
>>> @@ -1078,6 +1080,8 @@ static int __init intel_pstate_setup(char *str)
>>>
>>>    if (!strcmp(str, "disable"))
>>>        no_load = 1;
>>> +    if (!strcmp(str, "force"))
>>> +        force_load = 1;
>>>    return 0;
>>> }
>>> early_param("intel_pstate", intel_pstate_setup);
>>
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