linux-kernel - Re: [PATCH] Revert "cpufreq: intel_pstate: Fix ->set_policy() interface for no

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Date:   Mon, 06 Aug 2018 09:49:29 -0700
From:   Srinivas Pandruvada <srinivas.pandruvada@...ux.intel.com>
To:     "Rafael J. Wysocki" <rafael@...nel.org>,
        Gabriele Mazzotta <gabriele.mzt@...il.com>
Cc:     "Rafael J. Wysocki" <rjw@...ysocki.net>,
        Len Brown <lenb@...nel.org>,
        Viresh Kumar <viresh.kumar@...aro.org>,
        Linux PM <linux-pm@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] Revert "cpufreq: intel_pstate: Fix ->set_policy()
 interface for no_turbo"

On Mon, 2018-08-06 at 10:30 +0200, Rafael J. Wysocki wrote:
> On Sat, Aug 4, 2018 at 7:31 PM, Gabriele Mazzotta
> <gabriele.mzt@...il.com> wrote:
> > On 04/08/2018 17:29, Gabriele Mazzotta wrote:
> > > This change does not take into account that some BIOSes change
> > > MSR_IA32_MISC_ENABLE_TURBO_DISABLE depending on the power source.
> > > If the turbo is disabled when the system boots, policy.max_freq
> > > is set to pstate.max_pstate. However, if the BIOS later enables
> > > the turbo, the CPU will never be able to run at
> > > pstate.turbo_pstate.
> > > 
> > > Since now intel_pstate_set_policy() does its calculations using
> > > pstate.max_freq and pstate.turbo_freq, we can always calculate
> > > cpuinfo.max_freq using pstate.turbo_pstate, thus allowing system
> > > with varying MSR_IA32_MISC_ENABLE_TURBO_DISABLE to run at full
> > > speed when the turbo is enabled.
> 
> Well, the problem with this approach is that always using
> pstate.turbo_pstate as the max causes the governor to overestimate
> the
> target frequency when the turbo range is not available (the target
> depends on the width of the entire available P-state range including
> turbo, so if the turbo range is not available, the number take into
> that computation is too large).
> 
> Are we expected to get notified when the BIOS updates
> MSR_IA32_MISC_ENABLE_TURBO_DISABLE?

Let's try this:
- boot with kernel command line 

intel_pstate=support_acpi_ppc dyndbg="file processor_perflib.c +p"
dyndbg="file intel_pstate.c +p"

and send dmesg after you change power sources.

- Also try with
intel_pstate=disable dyndbg="file processor_perflib.c +p"

and send dmesg.

Thanks,
Srinivas