linux-kernel - RE: [PATCH] cpufreq: intel_pstate: Implement passive mode with HWP enabled

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Date:   Sun, 2 Aug 2020 08:17:39 -0700
From:   "Doug Smythies" <dsmythies@...us.net>
To:     "'Rafael J. Wysocki'" <rafael@...nel.org>
Cc:     "'Rafael J. Wysocki'" <rjw@...ysocki.net>,
        "'Linux Documentation'" <linux-doc@...r.kernel.org>,
        "'LKML'" <linux-kernel@...r.kernel.org>,
        "'Peter Zijlstra'" <peterz@...radead.org>,
        "'Srinivas Pandruvada'" <srinivas.pandruvada@...ux.intel.com>,
        "'Giovanni Gherdovich'" <ggherdovich@...e.cz>,
        "'Francisco Jerez'" <francisco.jerez.plata@...el.com>,
        "'Linux PM'" <linux-pm@...r.kernel.org>
Subject: RE: [PATCH] cpufreq: intel_pstate: Implement passive mode with HWP enabled

Hi Rafael,

On 2020.07.19 04:43 Rafael J. Wysocki wrote:
> On Fri, Jul 17, 2020 at 3:37 PM Doug Smythies <dsmythies@...us.net> wrote:
> > On 2020.07.16 05:08 Rafael J. Wysocki wrote:
> > > On Wed, Jul 15, 2020 at 10:39 PM Doug Smythies <dsmythies@...us.net> wrote:
> > >> On 2020.07.14 11:16 Rafael J. Wysocki wrote:
> > >> >
> > >> > From: Rafael J. Wysocki <rafael.j.wysocki@...el.com>
> > >> ...
> > >> > Since the passive mode hasn't worked with HWP at all, and it is not going to
> > >> > the default for HWP systems anyway, I don't see any drawbacks related to making
> > >> > this change, so I would consider this as 5.9 material unless there are any
> > >> > serious objections.
> > >>
> > >> Good point.
> >
> > Actually, for those users that default to passive mode upon boot,
> > this would mean they would find themselves using this.
> > Also, it isn't obvious, from the typical "what driver and what governor"
> > inquiry.
> 
> So the change in behavior is that after this patch
> intel_pstate=passive doesn't imply no_hwp any more.
> 
> That's a very minor difference though and I'm not aware of any adverse
> effects it can cause on HWP systems anyway.

My point was, that it will now default to something where
testing has not been completed.

> The "what governor" is straightforward in the passive mode: that's
> whatever cpufreq governor has been selected.

I think you might have missed my point.
>From the normal methods of inquiry one does not know
if HWP is being used or not. Why? Because with
or without HWP one gets the same answers under:

/sys/devices/system/cpu/cpu*/cpufreq/scaling_driver
/sys/devices/system/cpu/cpu*/cpufreq/scaling_governor

... Doug