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From: "Rafael J. Wysocki" <rafael@kernel.org>
To: Viresh Kumar <viresh.kumar@linaro.org>
Cc: "Rafael J. Wysocki" <rafael@kernel.org>,
	Takashi Iwai <tiwai@suse.de>, Kyle Meyer <kyle.meyer@hpe.com>,
	"Rafael J. Wysocki" <rjw@rjwysocki.net>,
	Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
	Linux PM <linux-pm@vger.kernel.org>,
	linux-acpi@vegr.kernel.org
Subject: Re: [PATCH] acpi-cpufreq: Skip initialization if a cpufreq driver exists
Date: Mon, 7 Jun 2021 13:02:46 +0200	[thread overview]
Message-ID: <CAJZ5v0g-NMLa1UVYKpF2ehgk=6dJkKRonUY0AGw6HyRCDaQMmw@mail.gmail.com> (raw)
In-Reply-To: <CAOh2x==tXk2Lt_f14_azHNYG2mZzMb9-1b2YUVj=+i=-JLemdg@mail.gmail.com>

On Mon, Jun 7, 2021 at 9:26 AM Viresh Kumar <viresh.kumar@linaro.org> wrote:
>
> Hi Rafael,
>
> On Mon, May 24, 2021 at 7:47 PM Rafael J. Wysocki <rafael@kernel.org> wrote:
> > On Sat, May 22, 2021 at 12:19 AM Kyle Meyer <kyle.meyer@hpe.com> wrote:
>
> > > diff --git a/drivers/cpufreq/acpi-cpufreq.c b/drivers/cpufreq/acpi-cpufreq.c
> > > index 7e7450453714..e79a945369d1 100644
> > > --- a/drivers/cpufreq/acpi-cpufreq.c
> > > +++ b/drivers/cpufreq/acpi-cpufreq.c
> > > @@ -1003,7 +1003,7 @@ static int __init acpi_cpufreq_init(void)
> > >
> > >         /* don't keep reloading if cpufreq_driver exists */
> > >         if (cpufreq_get_current_driver())
> > > -               return -EEXIST;
> > > +               return 0;
> > >
> > >         pr_debug("%s\n", __func__);
> > >
> > > --
> >
> > Applied as 5.14 material with some edits in the subject and changelog, thanks!
>
> I am not sure how this is supposed to work. If we return 0 from
> acpi_cpufreq_init(),
> then the driver will never be used, since it's acpi_cpufreq_init()
> will never get
> called again later.

Unless the module is unloaded and loaded again, that is.

> cpufreq drivers don't follow the generic device/driver model where a driver gets
> probed again if a device appears and so this is broken.

It is broken anyway as per the changelog of this patch.

On systems with several hundred logical CPUs this really can be troublesome.

> Please revert this patch.

Well, you can argue that the problem at hand is outside the kernel and
so it's not a kernel's business to address it.

After all, systemd-udevd could learn to avoid attempting to load the
module again if it fails with -EEXIST, but I'm not sure how different
that really would be from what this patch does, in practice.

  reply	other threads:[~2021-06-07 11:03 UTC|newest]

Thread overview: 8+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-05-21 22:19 Kyle Meyer
2021-05-21 22:19 ` Kyle Meyer
2021-05-24 14:16 ` Rafael J. Wysocki
2021-06-07  7:25   ` Viresh Kumar
2021-06-07 11:02     ` Rafael J. Wysocki [this message]
2021-06-07 11:14       ` Viresh Kumar
  -- strict thread matches above, loose matches on Subject: below --
2021-05-18 19:34 kyle.meyer
2021-05-21 13:01 ` Rafael J. Wysocki

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