linux-kernel - RE: [RESEND PATCH V2 2/9] cpufreq: amd_pstate: add module parameter to load amd pstate EPP driver

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Date:   Thu, 20 Oct 2022 15:56:21 +0000
From:   "Yuan, Perry" <Perry.Yuan@....com>
To:     "Huang, Ray" <Ray.Huang@....com>
CC:     "rafael.j.wysocki@...el.com" <rafael.j.wysocki@...el.com>,
        "viresh.kumar@...aro.org" <viresh.kumar@...aro.org>,
        "Sharma, Deepak" <Deepak.Sharma@....com>,
        "Limonciello, Mario" <Mario.Limonciello@....com>,
        "Fontenot, Nathan" <Nathan.Fontenot@....com>,
        "Deucher, Alexander" <Alexander.Deucher@....com>,
        "Huang, Shimmer" <Shimmer.Huang@....com>,
        "Du, Xiaojian" <Xiaojian.Du@....com>,
        "Meng, Li (Jassmine)" <Li.Meng@....com>,
        "linux-pm@...r.kernel.org" <linux-pm@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: RE: [RESEND PATCH V2 2/9] cpufreq: amd_pstate: add module parameter
 to load amd pstate EPP driver

[AMD Official Use Only - General]

Hi Ray. 

> -----Original Message-----
> From: Huang, Ray <Ray.Huang@....com>
> Sent: Monday, October 17, 2022 5:47 PM
> To: Yuan, Perry <Perry.Yuan@....com>
> Cc: rafael.j.wysocki@...el.com; viresh.kumar@...aro.org; Sharma, Deepak
> <Deepak.Sharma@....com>; Limonciello, Mario
> <Mario.Limonciello@....com>; Fontenot, Nathan
> <Nathan.Fontenot@....com>; Deucher, Alexander
> <Alexander.Deucher@....com>; Huang, Shimmer
> <Shimmer.Huang@....com>; Du, Xiaojian <Xiaojian.Du@....com>; Meng,
> Li (Jassmine) <Li.Meng@....com>; linux-pm@...r.kernel.org; linux-
> kernel@...r.kernel.org
> Subject: Re: [RESEND PATCH V2 2/9] cpufreq: amd_pstate: add module
> parameter to load amd pstate EPP driver
> 
> On Tue, Oct 11, 2022 at 12:22:41AM +0800, Yuan, Perry wrote:
> > The amd_pstate mode parameter will allow user to select which amd
> > pstate working mode as booting mode, amd_pstate instance or
> amd_pstate_epp instance.
> >
> > 1) amd_pstate instance is depending on the target operation mode.
> > 2) amd_pstate_epp instance is depending on the set_policy operation
> mode.It
> >    is also called active mode that AMD SMU has EPP algorithm to control the
> >    CPU runtime frequency according to the EPP set value and workload.
> >
> 
> There is one concern here: how can the user know which kind of processor
> supports the EPP function in hardware?
> 
> Thanks,
> Ray

Checked with internal team, I was told that EPP is part of the CPPC implementation, 
The Pstate driver already check if the cppc valid when driver loading, we do not need to check the epp again. 

Perry.

> 
> > Signed-off-by: Perry Yuan <Perry.Yuan@....com>
> > ---
> >  drivers/cpufreq/amd-pstate.c | 4 ++++
> >  1 file changed, 4 insertions(+)
> >
> > diff --git a/drivers/cpufreq/amd-pstate.c
> > b/drivers/cpufreq/amd-pstate.c index f52b8f2fe529..2d28f458589c 100644
> > --- a/drivers/cpufreq/amd-pstate.c
> > +++ b/drivers/cpufreq/amd-pstate.c
> > @@ -63,6 +63,10 @@ module_param(shared_mem, bool, 0444);
> > MODULE_PARM_DESC(shared_mem,
> >  		 "enable amd-pstate on processors with shared memory
> solution
> > (false = disabled (default), true = enabled)");
> >
> > +static bool epp = false;
> > +module_param(epp, bool, 0444);
> > +MODULE_PARM_DESC(epp, "Enable energy performance preference (EPP)
> > +control");
> > +
> >  static struct cpufreq_driver amd_pstate_driver;
> >
> >  /**
> > --
> > 2.34.1
> >