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

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Message-ID: <004601d66bb6$199ce1a0$4cd6a4e0$@net>
Date:   Wed, 5 Aug 2020 22:54:47 -0700
From:   "Doug Smythies" <dsmythies@...us.net>
To:     "'Rafael J. Wysocki'" <rjw@...ysocki.net>
Cc:     "'Rafael J. Wysocki'" <rafael@...nel.org>,
        "'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

On 2020.08.03 10:09 Rafael J. Wysocki wrote:
> On Sunday, August 2, 2020 5:17:39 PM CEST Doug Smythies wrote:
> > 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
> 
> Yes, but this is also the case in the active mode, isn't it?

Yes, fair enough.
But we aren't changing what it means by default
between kernel 5.8 and 5.9-rc1.

... Doug