linux-kernel - Re: [PATCH v2 2/2] cpufreq: Specify default governor on command line

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <CAJZ5v0g=+2OFKVk2ZnmK-33knUwqcaOOQ+q9ZWnmeoBD9KOX9g@mail.gmail.com>
Date:   Thu, 25 Jun 2020 13:44:34 +0200
From:   "Rafael J. Wysocki" <rafael@...nel.org>
To:     Viresh Kumar <viresh.kumar@...aro.org>
Cc:     Quentin Perret <qperret@...gle.com>,
        "Rafael J. Wysocki" <rjw@...ysocki.net>,
        "Rafael J. Wysocki" <rafael@...nel.org>,
        Arnd Bergmann <arnd@...db.de>,
        Michael Ellerman <mpe@...erman.id.au>,
        Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        Paul Mackerras <paulus@...ba.org>,
        Ingo Molnar <mingo@...hat.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Juri Lelli <juri.lelli@...hat.com>,
        Vincent Guittot <vincent.guittot@...aro.org>,
        linuxppc-dev <linuxppc-dev@...ts.ozlabs.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Linux PM <linux-pm@...r.kernel.org>,
        "Cc: Android Kernel" <kernel-team@...roid.com>,
        Todd Kjos <tkjos@...gle.com>, adharmap@...eaurora.org
Subject: Re: [PATCH v2 2/2] cpufreq: Specify default governor on command line

On Thu, Jun 25, 2020 at 1:36 PM Viresh Kumar <viresh.kumar@...aro.org> wrote:
>
> After your last email (reply to my patch), I noticed a change which
> isn't required. :)
>
> On 23-06-20, 15:21, Quentin Perret wrote:
> > diff --git a/drivers/cpufreq/cpufreq.c b/drivers/cpufreq/cpufreq.c
> > index 0128de3603df..4b1a5c0173cf 100644
> > --- a/drivers/cpufreq/cpufreq.c
> > +++ b/drivers/cpufreq/cpufreq.c
> > @@ -50,6 +50,9 @@ static LIST_HEAD(cpufreq_governor_list);
> >  #define for_each_governor(__governor)                                \
> >       list_for_each_entry(__governor, &cpufreq_governor_list, governor_list)
> >
> > +static char cpufreq_param_governor[CPUFREQ_NAME_LEN];
> > +static struct cpufreq_governor *default_governor;
> > +
> >  /**
> >   * The "cpufreq driver" - the arch- or hardware-dependent low
> >   * level driver of CPUFreq support, and its spinlock. This lock
> > @@ -1055,7 +1058,6 @@ __weak struct cpufreq_governor *cpufreq_default_governor(void)
> >
> >  static int cpufreq_init_policy(struct cpufreq_policy *policy)
> >  {
> > -     struct cpufreq_governor *def_gov = cpufreq_default_governor();
> >       struct cpufreq_governor *gov = NULL;
> >       unsigned int pol = CPUFREQ_POLICY_UNKNOWN;
> >
> > @@ -1065,8 +1067,8 @@ static int cpufreq_init_policy(struct cpufreq_policy *policy)
> >               if (gov) {
> >                       pr_debug("Restoring governor %s for cpu %d\n",
> >                                policy->governor->name, policy->cpu);
> > -             } else if (def_gov) {
> > -                     gov = def_gov;
> > +             } else if (default_governor) {
> > +                     gov = default_governor;
> >               } else {
> >                       return -ENODATA;
> >               }
>
>
> > @@ -1074,8 +1076,8 @@ static int cpufreq_init_policy(struct cpufreq_policy *policy)
> >               /* Use the default policy if there is no last_policy. */
> >               if (policy->last_policy) {
> >                       pol = policy->last_policy;
> > -             } else if (def_gov) {
> > -                     pol = cpufreq_parse_policy(def_gov->name);
> > +             } else if (default_governor) {
> > +                     pol = cpufreq_parse_policy(default_governor->name);
>
> This change is not right IMO. This part handles the set-policy case,
> where there are no governors. Right now this code, for some reasons
> unknown to me, forcefully uses the default governor set to indicate
> the policy, which is not a great idea in my opinion TBH. This doesn't
> and shouldn't care about governor modules and should only be looking
> at strings instead of governor pointer.

Sounds right.

> Rafael, I even think we should remove this code completely and just
> rely on what the driver has sent to us. Using the selected governor
> for set policy drivers is very confusing and also we shouldn't be
> forced to compiling any governor for the set-policy case.

Well, AFAICS the idea was to use the default governor as a kind of
default policy proxy, but I agree that strings should be sufficient
for that.

I'll have a look at what to do with that code.