linux-kernel - Re: [PATCH 2/8] cpufreq: Fix misplaced call to cpufreq_update

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Date:	Mon, 15 Jul 2013 13:37:35 +0200
From:	"Rafael J. Wysocki" <rjw@...k.pl>
To:	"Srivatsa S. Bhat" <srivatsa.bhat@...ux.vnet.ibm.com>
Cc:	Viresh Kumar <viresh.kumar@...aro.org>, toralf.foerster@....de,
	robert.jarzmik@...el.com, durgadoss.r@...el.com,
	tianyu.lan@...el.com, lantianyu1986@...il.com,
	dirk.brandewie@...il.com, stern@...land.harvard.edu,
	linux-pm@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/8] cpufreq: Fix misplaced call to cpufreq_update_policy()

On Monday, July 15, 2013 11:50:24 AM Srivatsa S. Bhat wrote:
> On 07/12/2013 12:36 PM, Viresh Kumar wrote:
> > On 12 July 2013 03:45, Srivatsa S. Bhat
> > <srivatsa.bhat@...ux.vnet.ibm.com> wrote:
> >> The call to cpufreq_update_policy() is placed in the CPU hotplug callback
> >> of cpufreq_stats, which has a higher priority than the CPU hotplug callback
> >> of cpufreq-core. As a result, during CPU_ONLINE/CPU_ONLINE_FROZEN, we end up
> >> calling cpufreq_update_policy() *before* calling cpufreq_add_dev() !
> >> And for uninitialized CPUs, it just returns silently, not doing anything.
> > 
> > Hmm..
> > 
> >> To add to it, cpufreq_stats is not even the right place to call
> >> cpufreq_update_policy() to begin with. The cpufreq core ought to handle
> >> this in its own callback, from an elegance/relevance perspective.
> >>
> >> So move the invocation of cpufreq_update_policy() to cpufreq_cpu_callback,
> >> and place it *after* cpufreq_add_dev().
> >>
> >> Signed-off-by: Srivatsa S. Bhat <srivatsa.bhat@...ux.vnet.ibm.com>
> >> ---
> >>
> >>  drivers/cpufreq/cpufreq.c       |    1 +
> >>  drivers/cpufreq/cpufreq_stats.c |    6 ------
> >>  2 files changed, 1 insertion(+), 6 deletions(-)
> >>
> >> diff --git a/drivers/cpufreq/cpufreq.c b/drivers/cpufreq/cpufreq.c
> >> index ccc6eab..f8c3100 100644
> >> --- a/drivers/cpufreq/cpufreq.c
> >> +++ b/drivers/cpufreq/cpufreq.c
> >> @@ -1943,6 +1943,7 @@ static int __cpuinit cpufreq_cpu_callback(struct notifier_block *nfb,
> >>                 case CPU_ONLINE:
> >>                 case CPU_ONLINE_FROZEN:
> >>                         cpufreq_add_dev(dev, NULL);
> >> +                       cpufreq_update_policy(cpu);
> > 
> > Do we need to call this for every hotplug of cpu? I am not
> > talking about suspend/resume here.
> > 
> 
> I don't think we need to, but I think it would be better to postpone
> optimizations until all the cpufreq regressions get fixed. Later perhaps
> we could revisit these minor optimizations if desired.

Agreed.

Thanks,
Rafael


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