linux-kernel - Re: [PATCH v2] cpufreq: intel_pstate: Add Icelake servers support in no-HWP mode

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Date:   Tue, 07 Sep 2021 19:04:33 -0700
From:   Srinivas Pandruvada <srinivas.pandruvada@...ux.intel.com>
To:     Doug Smythies <dsmythies@...us.net>
Cc:     Giovanni Gherdovich <ggherdovich@...e.cz>,
        "Rafael J . Wysocki" <rjw@...ysocki.net>,
        Viresh Kumar <viresh.kumar@...aro.org>,
        Len Brown <lenb@...nel.org>,
        Linux PM list <linux-pm@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2] cpufreq: intel_pstate: Add Icelake servers support
 in no-HWP mode

On Tue, 2021-09-07 at 13:16 -0700, Doug Smythies wrote:
> Hi Srinivas, Thank you for your reply.
> 
> On Tue, Sep 7, 2021 at 9:01 AM Srinivas Pandruvada
> <srinivas.pandruvada@...ux.intel.com> wrote:
> > On Tue, 2021-09-07 at 08:45 -0700, Doug Smythies wrote:
> > > 
> > > Recent ASUS BIOS updates have changed the default system
> > > response for this old thread, rendering "intel_pstate=no_hwp"
> > > useless.
> > > 
> > > It also raises a question: If BIOS has forced HWP, then how do we
> > > prevent the acpi-cpufreq driver from being used? Read on.
> > 
> > Does BIOS has option to enable Intel speed shift with no legacy
> > support?
> > Then this option will not populate ACPI _PSS table.
> 
> The option is there no matter what.
> I have tried every variation of legacy or no legacy that
> I can find. Currently:
> Current boot mode:   UEFI Firmware mode
> SecureBoot:          disabled
> 
> > 
> > > 
> > > On Fri, May 14, 2021 at 3:12 PM Doug Smythies < 
> > > dsmythies@...us.net>
> > > wrote:
> > > > 
> > > > On Fri, May 14, 2021 at 1:33 PM Giovanni Gherdovich <
> > > > ggherdovich@...e.cz> wrote:
> > > > > On Fri, 2021-05-14 at 08:31 -0700, Doug Smythies wrote:
> > > ...
> > > > > 
> ...
> > > Previous correspondence was with BIOS version 1003. There have
> > > been 3
> > > BIOS
> > > releases since then (at least that I know of), 2103, 2201, 2301,
> > > and
> > > all of them
> > > have changed the behaviour of the "Auto" setting for Intel Speed
> > > Shift
> > > Technology BIOS setting, forcing it on upon transfer of control
> > > to
> > > the OS.
> > > 
> > > Where with "intel_pstate=no_hwp" one used to get 0 for
> > > MSR_PM_ENABLE
> > > (0x770) they now get 1.
> > 
> > So they are forcing Out of band OOB mode.
> > Does bit 8 or 18 in MSR 0x1aa is set?
> 
> No.

So there is no legacy path. I think you are working with their support.
In HWP mode does setting scaling min/max frequency has any impact?

Thanks,
Srinivas

> 
> Here is the output from my msr reader/decoder program.
> Kernel 5.14 (unpatched).
> intel_pstate=disable
> BIOS setting "Auto" for Intel Speed Shift,
> Driver: acpi-cpufreq
> 
> doug@s19:~$ sudo c/msr-decoder
> How many CPUs?: 12
> 8.) 0x198: IA32_PERF_STATUS     : CPU 0-11 :  45 :  45 :  45 :  45 :
> 45 :  45 :  45 :  45 :  45 :  45 :  45 :  45 :
> B.) 0x770: IA32_PM_ENABLE: 1 : HWP enable
> 1.) 0x19C: IA32_THERM_STATUS: 88450000
> 2.) 0x1AA: MSR_MISC_PWR_MGMT: 401CC0 EIST enabled Coordination
> enabled
> OOB Bit 8 reset OOB Bit 18 reset
> 3.) 0x1B1: IA32_PACKAGE_THERM_STATUS: 88410000
> 4.) 0x64F: MSR_CORE_PERF_LIMIT_REASONS: 0
> A.) 0x1FC: MSR_POWER_CTL: 3C005D : C1E disable : EEO disable : RHO
> disable
> 5.) 0x771: IA32_HWP_CAPABILITIES (performance): 10B2930 : high 48 :
> guaranteed 41 : efficient 11 : lowest 1
> 6.) 0x774: IA32_HWP_REQUEST:    CPU 0-11 :
>     raw: 80003001 : 80003001 : 80003001 : 80003001 : 80003001 :
> 80003001 : 80003001 : 80003001 : 80003001 : 80003001 : 80003001 :
> 80003001 :
>     min:        1 :        1 :        1 :        1 :        1 :
> 1 :        1 :        1 :        1 :        1 :        1 :        1 :
>     max:       48 :       48 :       48 :       48 :       48 :
> 48 :       48 :       48 :       48 :       48 :       48 :       48
> :
>     des:        0 :        0 :        0 :        0 :        0 :
> 0 :        0 :        0 :        0 :        0 :        0 :        0 :
>     epp:      128 :      128 :      128 :      128 :      128 :
> 128 :      128 :      128 :      128 :      128 :      128 :      128
> :
>     act:        0 :        0 :        0 :        0 :        0 :
> 0 :        0 :        0 :        0 :        0 :        0 :        0 :
> 7.) 0x777: IA32_HWP_STATUS: 0 : high 0 : guaranteed 0 : efficient 0 :
> lowest 0
> 
> ...
> 
> ... Doug