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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>,
	Rafael Wysocki <rjw@rjwysocki.net>,
	Srinivas Pandruvada <srinivas.pandruvada@linux.intel.com>,
	Len Brown <lenb@kernel.org>, Linux PM <linux-pm@vger.kernel.org>,
	Vincent Guittot <vincent.guittot@linaro.org>,
	Dirk Brandewie <dirk.brandewie@gmail.com>,
	Linux Kernel Mailing List <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH V3 2/3] cpufreq: intel_pstate: Migrate away from ->stop_cpu() callback
Date: Mon, 21 Jun 2021 16:26:31 +0200	[thread overview]
Message-ID: <CAJZ5v0iHDk6Te0KogYToWSyquNcpS2edQzp1UbW3KFAVL31Hnw@mail.gmail.com> (raw)
In-Reply-To: <CAJZ5v0jM3nusF1fjcMHLRHPk2PhFErhBXijpWHiSNnunzPFjeA@mail.gmail.com>

On Mon, Jun 21, 2021 at 4:17 PM Rafael J. Wysocki <rafael@kernel.org> wrote:
>
> On Mon, Jun 21, 2021 at 5:09 AM Viresh Kumar <viresh.kumar@linaro.org> wrote:
> >
> > On 18-06-21, 14:00, Rafael J. Wysocki wrote:
> > > On Fri, Jun 18, 2021 at 5:22 AM Viresh Kumar <viresh.kumar@linaro.org> wrote:
> > > >
> > > > commit 367dc4aa932b ("cpufreq: Add stop CPU callback to cpufreq_driver
> > > > interface") added the stop_cpu() callback to allow the drivers to do
> > > > clean up before the CPU is completely down and its state can't be
> > > > modified.
> > > >
> > > > At that time the CPU hotplug framework used to call the cpufreq core's
> > > > registered notifier for different events like CPU_DOWN_PREPARE and
> > > > CPU_POST_DEAD. The stop_cpu() callback was called during the
> > > > CPU_DOWN_PREPARE event.
> > > >
> > > > This is no longer the case, cpuhp_cpufreq_offline() is called only once
> > > > by the CPU hotplug core now and we don't really need to separately
> > > > call stop_cpu() for cpufreq drivers.
> > > >
> > > > Migrate to using the exit() and offline() callbacks instead of
> > > > stop_cpu().
> > > >
> > > > We need to clear util hook from both the callbacks, exit() and
> > > > offline(), since it is possible that only exit() gets called sometimes
> > > > (specially on errors) or both get called at other times.
> > > > intel_pstate_clear_update_util_hook() anyway have enough protection in
> > > > place if it gets called a second time and will return early then.
> > > >
> > > > Cc: Dirk Brandewie <dirk.brandewie@gmail.com>
> > > > Signed-off-by: Viresh Kumar <viresh.kumar@linaro.org>
> > > > ---
> > > > V2->V3:
> > > > - Update intel_pstate_cpu_offline() as well.
> > > > - Improved commit log.
> > > >
> > > >  drivers/cpufreq/intel_pstate.c | 12 ++++--------
> > > >  1 file changed, 4 insertions(+), 8 deletions(-)
> > > >
> > > > diff --git a/drivers/cpufreq/intel_pstate.c b/drivers/cpufreq/intel_pstate.c
> > > > index 0e69dffd5a76..8f8a2d9d7daa 100644
> > > > --- a/drivers/cpufreq/intel_pstate.c
> > > > +++ b/drivers/cpufreq/intel_pstate.c
> > > > @@ -2335,6 +2335,8 @@ static int intel_pstate_cpu_offline(struct cpufreq_policy *policy)
> > > >
> > > >         pr_debug("CPU %d going offline\n", cpu->cpu);
> > > >
> > > > +       intel_pstate_clear_update_util_hook(policy->cpu);
> > > > +
> > > >         if (cpu->suspended)
> > > >                 return 0;
> > > >
> > > > @@ -2374,17 +2376,12 @@ static int intel_pstate_cpu_online(struct cpufreq_policy *policy)
> > > >         return 0;
> > > >  }
> > > >
> > > > -static void intel_pstate_stop_cpu(struct cpufreq_policy *policy)
> > > > -{
> > > > -       pr_debug("CPU %d stopping\n", policy->cpu);
> > > > -
> > > > -       intel_pstate_clear_update_util_hook(policy->cpu);
> > > > -}
> > > > -
> > > >  static int intel_pstate_cpu_exit(struct cpufreq_policy *policy)
> > > >  {
> > > >         pr_debug("CPU %d exiting\n", policy->cpu);
> > > >
> > > > +       intel_pstate_clear_update_util_hook(policy->cpu);
> > >
> > > This change is not needed now, because ->offline always runs before
> > > ->exit if present.
> >
> > Not necessarily, we don't call ->offline() for many error paths in
> > cpufreq_online().
>
> I guess you mean the error paths in cpufreq_offline()?

s/offline/online/

> IMO this is confusing/broken, because ->offline should always be
> called after ->online has returned success.
>
> > offline() only comes into play after driver is registered properly once.
>
> The relevant intel_pstate case is a ->setpolicy driver where
> ->setpolicy or ->online, if successful, need to be followed by
> ->offline.
>
> If ->setpolicy is successful in the cpufreq_online() path, the entire
> cpufreq_online() is successful and the error paths in question are not
> executed.
>
> So the change I was talking about is not needed AFAICS.

  reply	other threads:[~2021-06-21 14:26 UTC|newest]

Thread overview: 13+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-06-16  6:40 [PATCH V2 0/3] cpufreq: " Viresh Kumar
2021-06-16  6:40 ` Viresh Kumar
2021-06-16  6:40 ` [PATCH V2 1/3] cpufreq: cppc: Migrate to ->exit() callback instead of ->stop_cpu() Viresh Kumar
2021-06-16  6:40 ` [PATCH V2 2/3] cpufreq: intel_pstate: " Viresh Kumar
2021-06-17 13:27   ` Rafael J. Wysocki
2021-06-18  3:22   ` [PATCH V3 2/3] cpufreq: intel_pstate: Migrate away from ->stop_cpu() callback Viresh Kumar
2021-06-18 12:00     ` Rafael J. Wysocki
2021-06-21  3:09       ` Viresh Kumar
2021-06-21 14:17         ` Rafael J. Wysocki
2021-06-21 14:26           ` Rafael J. Wysocki [this message]
2021-06-21 17:14             ` Rafael J. Wysocki
2021-06-16  6:40 ` [PATCH V2 3/3] cpufreq: powerenv: Migrate to ->exit() callback instead of ->stop_cpu() Viresh Kumar
2021-06-16  6:40   ` Viresh Kumar

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