linux-kernel - Re: [PATCH V3 1/6] cpufreq: suspend governors on system suspend/hibernate

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Date:	Wed, 27 Nov 2013 02:42:27 +0100
From:	"Rafael J. Wysocki" <rjw@...ysocki.net>
To:	Viresh Kumar <viresh.kumar@...aro.org>
Cc:	Lists linaro-kernel <linaro-kernel@...ts.linaro.org>,
	Patch Tracking <patches@...aro.org>,
	"cpufreq@...r.kernel.org" <cpufreq@...r.kernel.org>,
	"linux-pm@...r.kernel.org" <linux-pm@...r.kernel.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Nishanth Menon <nm@...com>,
	Stephen Warren <swarren@...dotorg.org>,
	Kgene Kim <kgene.kim@...sung.com>,
	linux-samsung-soc <linux-samsung-soc@...r.kernel.org>,
	linux-tegra@...r.kernel.org, jinchoi@...adcom.com,
	Lan Tianyu <tianyu.lan@...el.com>,
	Sebastian Capella <sebastian.capella@...aro.org>,
	Jonghwan Choi <jhbird.choi@...sung.com>
Subject: Re: [PATCH V3 1/6] cpufreq: suspend governors on system suspend/hibernate

On Tuesday, November 26, 2013 09:23:15 PM Rafael J. Wysocki wrote:
> On Tuesday, November 26, 2013 07:56:19 AM Viresh Kumar wrote:
> > On 26 November 2013 04:59, Rafael J. Wysocki <rjw@...ysocki.net> wrote:
> > >> @@ -1259,6 +1262,8 @@ int dpm_suspend(pm_message_t state)
> > >>
> > >>       might_sleep();
> > >>
> > >> +     cpufreq_suspend();
> > >> +
> > >>
> > >>       mutex_lock(&dpm_list_mtx);
> > >>       pm_transition = state;
> > >>       async_error = 0;
> > >
> > > Shouldn't it do cpufreq_resume() on errors?
> > 
> > Yes and this is already done I believe. In case dpm_suspend() fails,
> > dpm_resume() gets called. Isn't it?
> 
> OK
> 
> > >> diff --git a/drivers/cpufreq/cpufreq.c b/drivers/cpufreq/cpufreq.c
> > >> +void cpufreq_suspend(void)
> > >> +{
> > >> +     struct cpufreq_policy *policy;
> > >> +
> > >> +     if (!has_target())
> > >> +             return;
> > >> +
> > >> +     pr_debug("%s: Suspending Governors\n", __func__);
> > >> +
> > >> +     list_for_each_entry(policy, &cpufreq_policy_list, policy_list)
> > >> +             if (__cpufreq_governor(policy, CPUFREQ_GOV_STOP))
> > >> +                     pr_err("%s: Failed to stop governor for policy: %p\n",
> > >> +                                     __func__, policy);
> > >
> > > This appears to be racy.  Is it really racy, or just seemingly?
> > 
> > Why does it look racy to you? Userspace should be frozen by now,
> > policy_list should be stable as well as nobody would touch it.
> 
> You're stopping governors while they may be in use in principle.  Do we have
> suitable synchronization in place for that?

Anyway, if you did what I asked you to do and put the cpufreq suspend/resume
into dpm_suspend/resume_noirq(), I'd probably take this for 3.13.  However,
since you've decided to put those things somewhere else thus making the
change much more intrusive, I can only queue it up for 3.14.

This means I'm going to take the Tianyu's patch as a stop gap for 3.13.

Thanks!

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