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

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Message-Id: <CEF8DE9B-262F-4EED-B982-9CD52617EEC5@gmail.com>
Date:	Sat, 6 Dec 2014 10:16:37 +0800
From:	ethan <ethan.kernel@...il.com>
To:	Linda Knippers <linda.knippers@...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.

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. 

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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