Re: [PATCH v6 2/8] cpufreq: Add boost frequency support in core

Rafael J. Wysocki
2013-07-26T12:36:08Z

On Friday, July 26, 2013 10:33:21 AM Lukasz Majewski wrote:
> On Fri, 26 Jul 2013 12:47:15 +0530 Viresh Kumar wrote,
> > On 25 July 2013 22:03, Lukasz Majewski <l.majewski@samsung.com> wrote:
> > > diff --git a/drivers/cpufreq/cpufreq.c b/drivers/cpufreq/cpufreq.c
> >
> > > /*********************************************************************
> > > + *
> > > BOOST *
> > > +
> > > *********************************************************************/
> > > +static int cpufreq_boost_set_sw(int state) +{
> > > + struct cpufreq_frequency_table *freq_table;
> > > + struct cpufreq_policy *policy;
> > > + int ret = -EINVAL;
> > > +
> > > + list_for_each_entry(policy, &cpufreq_policy_list,
> > > policy_list) {
> > > + freq_table =
> > > cpufreq_frequency_get_table(policy->cpu);
> > > + if (freq_table) {
> > > + ret =
> > > cpufreq_frequency_table_cpuinfo(policy,
> > > + freq_table);
> > > + if (!ret) {
> > > + policy->user_policy.max =
> > > policy->max;
> > > + __cpufreq_governor(policy,
> > > CPUFREQ_GOV_LIMITS);
> > > + }
> > > + }
> > > + }
> > > +
> > > + return ret;
> > > +}
> > > +
> > > +int cpufreq_boost_trigger_state(int state)
> > > +{
> > > + unsigned long flags;
> > > + int ret = 0;
> > > +
> > > + if (cpufreq_driver->boost_enabled == state)
> > > + return 0;
> > > +
> > > + write_lock_irqsave(&cpufreq_driver_lock, flags);
> > > + cpufreq_driver->boost_enabled = state;
> > > + write_unlock_irqrestore(&cpufreq_driver_lock, flags);
> ^^^^^^^^^^^^^^^^^^^^ [*]
> >
> > Not sure if we should leave the lock at this point of time, as we
> > haven't enabled boost until now.
>
> The problem here is with the cpufreq_driver->set_boost() call.
>
> I tried to avoid acquiring lock at one function and release it at
> another (in this case cpufreq_boost_set_sw), especially since the
> __cpufreq_governor() acquires its own lock - good place for deadlock.
>
> Is it OK for you to grab lock at one function
> (cpufreq_boost_trigger_state()) and then at other function
> (cpufreq_boost_set_sw) release it before calling __cpufreq_governor()
> and grab it again after its completion?

It generally is better to avoid doing that, although it is not unheard of.

Thanks,
Rafael

--
I speak only for myself.
Rafael J. Wysocki, Intel Open Source Technology Center.